pgsql: Clarify some error messages about duplicate things.

Log Message:
-----------
Clarify some error messages about duplicate things.

Modified Files:
--------------
    pgsql/src/backend/access/common:
        reloptions.c (r1.4 -> r1.5)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/reloptions.c.diff?r1=1.4&r2=1.5)
    pgsql/src/backend/access/nbtree:
        nbtinsert.c (r1.157 -> r1.158)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtinsert.c.diff?r1=1.157&r2=1.158)
    pgsql/src/backend/catalog:
        heap.c (r1.321 -> r1.322)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/heap.c.diff?r1=1.321&r2=1.322)
    pgsql/src/backend/commands:
        tablecmds.c (r1.226 -> r1.227)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/tablecmds.c.diff?r1=1.226&r2=1.227)
    pgsql/src/test/regress/expected:
        alter_table.out (r1.102 -> r1.103)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/alter_table.out.diff?r1=1.102&r2=1.103)
        arrays.out (r1.33 -> r1.34)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/arrays.out.diff?r1=1.33&r2=1.34)
        create_index.out (r1.24 -> r1.25)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/create_index.out.diff?r1=1.24&r2=1.25)
        inherit.out (r1.20 -> r1.21)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/inherit.out.diff?r1=1.20&r2=1.21)
        plpgsql.out (r1.54 -> r1.55)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/plpgsql.out.diff?r1=1.54&r2=1.55)
        transactions.out (r1.15 -> r1.16)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/transactions.out.diff?r1=1.15&r2=1.16)
        uuid.out (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/uuid.out.diff?r1=1.2&r2=1.3)
    pgsql/src/test/regress/output:
        constraints.source (r1.42 -> r1.43)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/output/constraints.source.diff?r1=1.42&r2=1.43)
        tablespace.source (r1.4 -> r1.5)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/output/tablespace.source.diff?r1=1.4&r2=1.5)