pgsql: Backpatch fix for buffer overrun in parsing refcursor parameters

Log Message:
-----------
Backpatch fix for buffer overrun in parsing refcursor parameters to
REL7_2_STABLE.

Tags:
----
REL7_2_STABLE

Modified Files:
--------------
pgsql/src/pl/plpgsql/src:
gram.y (r1.29.2.1 -> r1.29.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/gram.y.diff?r1=1.29.2.1&r2=1.29.2.2)