pgsql: Remove support for Kerberos V4.

Log Message:
-----------
Remove support for Kerberos V4. It seems no one is using this, it has
some security issues, and upstream has declared it "dead". Patch from
Magnus Hagander, minor editorialization from Neil Conway.

Modified Files:
--------------
    pgsql:
        configure (r1.439 -> r1.440)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.diff?r1=1.439&r2=1.440)
        configure.in (r1.412 -> r1.413)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.in.diff?r1=1.412&r2=1.413)
    pgsql/doc/src/sgml:
        client-auth.sgml (r1.81 -> r1.82)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/client-auth.sgml.diff?r1=1.81&r2=1.82)
        installation.sgml (r1.237 -> r1.238)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml.diff?r1=1.237&r2=1.238)
        libpq.sgml (r1.187 -> r1.188)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml.diff?r1=1.187&r2=1.188)
        protocol.sgml (r1.60 -> r1.61)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/protocol.sgml.diff?r1=1.60&r2=1.61)
    pgsql/src/backend/libpq:
        auth.c (r1.125 -> r1.126)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c.diff?r1=1.125&r2=1.126)
        hba.c (r1.141 -> r1.142)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c.diff?r1=1.141&r2=1.142)
        pg_hba.conf.sample (r1.57 -> r1.58)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pg_hba.conf.sample.diff?r1=1.57&r2=1.58)
    pgsql/src/include:
        pg_config.h.in (r1.84 -> r1.85)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config.h.in.diff?r1=1.84&r2=1.85)
        port.h (r1.75 -> r1.76)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/port.h.diff?r1=1.75&r2=1.76)
    pgsql/src/include/libpq:
        auth.h (r1.28 -> r1.29)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/auth.h.diff?r1=1.28&r2=1.29)
        hba.h (r1.36 -> r1.37)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/hba.h.diff?r1=1.36&r2=1.37)
        pqcomm.h (r1.96 -> r1.97)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/pqcomm.h.diff?r1=1.96&r2=1.97)
    pgsql/src/interfaces/libpq:
        Makefile (r1.133 -> r1.134)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/Makefile.diff?r1=1.133&r2=1.134)
        fe-auth.c (r1.101 -> r1.102)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.c.diff?r1=1.101&r2=1.102)
        fe-auth.h (r1.20 -> r1.21)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.h.diff?r1=1.20&r2=1.21)
        fe-connect.c (r1.312 -> r1.313)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c.diff?r1=1.312&r2=1.313)
        libpq-int.h (r1.103 -> r1.104)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h.diff?r1=1.103&r2=1.104)