pgsql-server: Come to think of it, functions in FROM have the same

Log Message:
-----------
Come to think of it, functions in FROM have the same syntactic restriction
as CREATE INDEX did, and can be fixed the same way, for another small
improvement in usability and reduction in grammar size.

Modified Files:
--------------
    pgsql-server/src/backend/parser:
        gram.y (r2.476 -> r2.477)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/gram.y.diff?r1=2.476&r2=2.477)
        parse_clause.c (r1.136 -> r1.137)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/parse_clause.c.diff?r1=1.136&r2=1.137)
        parse_target.c (r1.125 -> r1.126)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/parse_target.c.diff?r1=1.125&r2=1.126)
    pgsql-server/src/include/parser:
        parse_target.h (r1.33 -> r1.34)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/parser/parse_target.h.diff?r1=1.33&r2=1.34)