Thread: pgsql: Throw error if a references a window that

Log Message:
-----------
Throw error if a <window definition> references a window that already has a
frame clause, as appears to be required by the fine print in the SQL spec.
Per discussion with Pavel, not doing so risks user confusion.

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        select.sgml (r1.115 -> r1.116)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/select.sgml?r1=1.115&r2=1.116)
    pgsql/doc/src/sgml:
        syntax.sgml (r1.128 -> r1.129)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/syntax.sgml?r1=1.128&r2=1.129)
    pgsql/src/backend/parser:
        parse_clause.c (r1.183 -> r1.184)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_clause.c?r1=1.183&r2=1.184)