pgsql: Implement the basic form of UNNEST, ie unnest(anyarray) returns

Log Message:
-----------
Implement the basic form of UNNEST, ie unnest(anyarray) returns setof
anyelement.  This lacks the WITH ORDINALITY option, as well as the multiple
input arrays option added in the most recent SQL specs.  But it's still a
pretty useful subset of the spec's functionality, and it is enough to
allow obsoleting contrib/intagg.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        func.sgml (r1.459 -> r1.460)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.459&r2=1.460)
    pgsql/src/backend/utils/adt:
        arrayfuncs.c (r1.149 -> r1.150)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/arrayfuncs.c?r1=1.149&r2=1.150)
    pgsql/src/include/catalog:
        catversion.h (r1.505 -> r1.506)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.505&r2=1.506)
        pg_proc.h (r1.527 -> r1.528)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.527&r2=1.528)
    pgsql/src/include/utils:
        array.h (r1.71 -> r1.72)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/array.h?r1=1.71&r2=1.72)
    pgsql/src/test/regress/expected:
        arrays.out (r1.44 -> r1.45)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/arrays.out?r1=1.44&r2=1.45)
    pgsql/src/test/regress/sql:
        arrays.sql (r1.33 -> r1.34)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/arrays.sql?r1=1.33&r2=1.34)