pgsql: Suppress a few 'uninitialized variable' warnings that gcc emits

Log Message:
-----------
Suppress a few 'uninitialized variable' warnings that gcc emits only at
-O3 or higher (presumably because it inlines more things). Per gripe
from Mark Mielke.

Modified Files:
--------------
pgsql/src/backend/access/nbtree:
nbtinsert.c (r1.145 -> r1.146)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtinsert.c.diff?r1=1.145&r2=1.146)
pgsql/src/backend/optimizer/path:
costsize.c (r1.168 -> r1.169)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/costsize.c.diff?r1=1.168&r2=1.169)
pgsql/src/backend/utils/adt:
timestamp.c (r1.168 -> r1.169)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/timestamp.c.diff?r1=1.168&r2=1.169)