pgsql: Add quote_literal(anyelement) to preserve (and, in fact, extend)

Log Message:
-----------
Add quote_literal(anyelement) to preserve (and, in fact, extend) a
useful consequence of the former liberal implicit casting to text;
namely that you can feed non-string values to quote_literal() and get
unsurprising results.  Per discussion.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        func.sgml (r1.411 -> r1.412)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.411&r2=1.412)
    pgsql/src/include/catalog:
        catversion.h (r1.438 -> r1.439)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.438&r2=1.439)
        pg_proc.h (r1.479 -> r1.480)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.479&r2=1.480)