pgsql: Prevent creating window functions with default arguments.

Prevent creating window functions with default arguments.

Insertion of default arguments doesn't work for window functions, which is
likely to cause a crash at runtime if the implementation code doesn't check
the number of actual arguments carefully.  It doesn't seem worth working
harder than this for pre-9.2 branches.

Branch
------
REL9_0_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/352ab596fa5a8a4ceec6d308ebae34176cc09c13

Modified Files
--------------
doc/src/sgml/syntax.sgml      |    7 +++++++
src/backend/catalog/pg_proc.c |    6 ++++++
2 files changed, 13 insertions(+)