pgsql: Fix PGXS conventions so that extensions can be built against

Log Message:
-----------
Fix PGXS conventions so that extensions can be built against Postgres
installations whose pg_config program does not appear first in the PATH.
Per gripe from Eddie Stanley and subsequent discussions with Fabien Coelho
and others.

Modified Files:
--------------
    pgsql/contrib/adminpack:
        Makefile (r1.4 -> r1.5)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/adminpack/Makefile.diff?r1=1.4&r2=1.5)
    pgsql/contrib/btree_gist:
        Makefile (r1.10 -> r1.11)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/btree_gist/Makefile.diff?r1=1.10&r2=1.11)
    pgsql/contrib/chkpass:
        Makefile (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/chkpass/Makefile.diff?r1=1.8&r2=1.9)
    pgsql/contrib/cube:
        Makefile (r1.19 -> r1.20)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/cube/Makefile.diff?r1=1.19&r2=1.20)
    pgsql/contrib/dblink:
        Makefile (r1.13 -> r1.14)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/Makefile.diff?r1=1.13&r2=1.14)
    pgsql/contrib/earthdistance:
        Makefile (r1.17 -> r1.18)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/earthdistance/Makefile.diff?r1=1.17&r2=1.18)
    pgsql/contrib/fuzzystrmatch:
        Makefile (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/fuzzystrmatch/Makefile.diff?r1=1.8&r2=1.9)
    pgsql/contrib/intagg:
        Makefile (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/intagg/Makefile.diff?r1=1.7&r2=1.8)
    pgsql/contrib/intarray:
        Makefile (r1.14 -> r1.15)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/intarray/Makefile.diff?r1=1.14&r2=1.15)
    pgsql/contrib/isn:
        Makefile (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/isn/Makefile.diff?r1=1.1&r2=1.2)
    pgsql/contrib/lo:
        Makefile (r1.15 -> r1.16)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/lo/Makefile.diff?r1=1.15&r2=1.16)
    pgsql/contrib/ltree:
        Makefile (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/ltree/Makefile.diff?r1=1.6&r2=1.7)
    pgsql/contrib/oid2name:
        Makefile (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/oid2name/Makefile.diff?r1=1.8&r2=1.9)
    pgsql/contrib/pageinspect:
        Makefile (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pageinspect/Makefile.diff?r1=1.1&r2=1.2)
    pgsql/contrib/pg_buffercache:
        Makefile (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_buffercache/Makefile.diff?r1=1.3&r2=1.4)
    pgsql/contrib/pg_freespacemap:
        Makefile (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_freespacemap/Makefile.diff?r1=1.2&r2=1.3)
    pgsql/contrib/pg_standby:
        Makefile (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_standby/Makefile.diff?r1=1.2&r2=1.3)
        pg_standby.c (r1.5 -> r1.6)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_standby/pg_standby.c.diff?r1=1.5&r2=1.6)
    pgsql/contrib/pg_trgm:
        Makefile (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_trgm/Makefile.diff?r1=1.7&r2=1.8)
    pgsql/contrib/pgbench:
        Makefile (r1.14 -> r1.15)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgbench/Makefile.diff?r1=1.14&r2=1.15)
    pgsql/contrib/pgcrypto:
        Makefile (r1.25 -> r1.26)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgcrypto/Makefile.diff?r1=1.25&r2=1.26)
    pgsql/contrib/pgrowlocks:
        Makefile (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgrowlocks/Makefile.diff?r1=1.3&r2=1.4)
    pgsql/contrib/pgstattuple:
        Makefile (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgstattuple/Makefile.diff?r1=1.7&r2=1.8)
    pgsql/contrib/seg:
        Makefile (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/seg/Makefile.diff?r1=1.18&r2=1.19)
    pgsql/contrib/spi:
        Makefile (r1.26 -> r1.27)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/spi/Makefile.diff?r1=1.26&r2=1.27)
    pgsql/contrib/sslinfo:
        Makefile (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/sslinfo/Makefile.diff?r1=1.8&r2=1.9)
    pgsql/contrib/tablefunc:
        Makefile (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tablefunc/Makefile.diff?r1=1.7&r2=1.8)
    pgsql/contrib/tsearch2:
        Makefile (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tsearch2/Makefile.diff?r1=1.18&r2=1.19)
    pgsql/contrib/tsearch2/ispell:
        Makefile (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tsearch2/ispell/Makefile.diff?r1=1.9&r2=1.10)
    pgsql/contrib/tsearch2/snowball:
        Makefile (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tsearch2/snowball/Makefile.diff?r1=1.9&r2=1.10)
    pgsql/contrib/tsearch2/wordparser:
        Makefile (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tsearch2/wordparser/Makefile.diff?r1=1.9&r2=1.10)
    pgsql/contrib/uuid-ossp:
        Makefile (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/uuid-ossp/Makefile.diff?r1=1.1&r2=1.2)
    pgsql/contrib/vacuumlo:
        Makefile (r1.15 -> r1.16)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/vacuumlo/Makefile.diff?r1=1.15&r2=1.16)
    pgsql/contrib/xml2:
        Makefile (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/xml2/Makefile.diff?r1=1.9&r2=1.10)
    pgsql/doc/src/sgml:
        xfunc.sgml (r1.128 -> r1.129)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/xfunc.sgml.diff?r1=1.128&r2=1.129)
    pgsql/src:
        Makefile.global.in (r1.236 -> r1.237)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/Makefile.global.in.diff?r1=1.236&r2=1.237)
    pgsql/src/makefiles:
        pgxs.mk (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/makefiles/pgxs.mk.diff?r1=1.9&r2=1.10)
    pgsql/src/tutorial:
        Makefile (r1.19 -> r1.20)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tutorial/Makefile.diff?r1=1.19&r2=1.20)