pgsql: More clearly document that most PostgreSQL utilities support

Log Message:
-----------
More clearly document that most PostgreSQL utilities support libpq
environment variables.  Backpatch to 8.2.X.

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        clusterdb.sgml (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/clusterdb.sgml.diff?r1=1.18&r2=1.19)
        createdb.sgml (r1.42 -> r1.43)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/createdb.sgml.diff?r1=1.42&r2=1.43)
        createlang.sgml (r1.38 -> r1.39)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/createlang.sgml.diff?r1=1.38&r2=1.39)
        createuser.sgml (r1.45 -> r1.46)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/createuser.sgml.diff?r1=1.45&r2=1.46)
        dropdb.sgml (r1.28 -> r1.29)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/dropdb.sgml.diff?r1=1.28&r2=1.29)
        droplang.sgml (r1.27 -> r1.28)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/droplang.sgml.diff?r1=1.27&r2=1.28)
        dropuser.sgml (r1.34 -> r1.35)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/dropuser.sgml.diff?r1=1.34&r2=1.35)
        initdb.sgml (r1.40 -> r1.41)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/initdb.sgml.diff?r1=1.40&r2=1.41)
        pg_controldata.sgml (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_controldata.sgml.diff?r1=1.9&r2=1.10)
        pg_ctl-ref.sgml (r1.38 -> r1.39)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_ctl-ref.sgml.diff?r1=1.38&r2=1.39)
        pg_dump.sgml (r1.95 -> r1.96)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_dump.sgml.diff?r1=1.95&r2=1.96)
        pg_dumpall.sgml (r1.65 -> r1.66)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_dumpall.sgml.diff?r1=1.65&r2=1.66)
        pg_restore.sgml (r1.68 -> r1.69)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_restore.sgml.diff?r1=1.68&r2=1.69)
        psql-ref.sgml (r1.183 -> r1.184)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/psql-ref.sgml.diff?r1=1.183&r2=1.184)
        reindexdb.sgml (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/reindexdb.sgml.diff?r1=1.2&r2=1.3)
        vacuumdb.sgml (r1.38 -> r1.39)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/vacuumdb.sgml.diff?r1=1.38&r2=1.39)