pgsql: Add string functions: concat(), concat_ws(), left(), right(), and

Log Message:
-----------
Add string functions: concat(), concat_ws(), left(), right(), and reverse().

Pavel Stehule, reviewed by me.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        func.sgml (r1.529 -> r1.530)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.529&r2=1.530)
    pgsql/src/backend/utils/adt:
        varlena.c (r1.179 -> r1.180)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/varlena.c?r1=1.179&r2=1.180)
    pgsql/src/include/catalog:
        catversion.h (r1.596 -> r1.597)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.596&r2=1.597)
        pg_proc.h (r1.580 -> r1.581)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.580&r2=1.581)
    pgsql/src/include/utils:
        builtins.h (r1.354 -> r1.355)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h?r1=1.354&r2=1.355)
    pgsql/src/test/regress/expected:
        text.out (r1.4 -> r1.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/text.out?r1=1.4&r2=1.5)
    pgsql/src/test/regress/sql:
        text.sql (r1.4 -> r1.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/text.sql?r1=1.4&r2=1.5)