pgsql: Modify hash_search() API to prevent future occurrences of the

Log Message:
-----------
Modify hash_search() API to prevent future occurrences of the error
spotted by Qingqing Zhou. The HASH_ENTER action now automatically
fails with elog(ERROR) on out-of-memory --- which incidentally lets
us eliminate duplicate error checks in quite a bunch of places. If
you really need the old return-NULL-on-out-of-memory behavior, you
can ask for HASH_ENTER_NULL. But there is now an Assert in that path
checking that you aren't hoping to get that behavior in a palloc-based
hash table.
Along the way, remove the old HASH_FIND_SAVE/HASH_REMOVE_SAVED actions,
which were not being used anywhere anymore, and were surely too ugly
and unsafe to want to see revived again.

Modified Files:
--------------
pgsql/contrib/dblink:
dblink.c (r1.41 -> r1.42)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/dblink.c.diff?r1=1.41&r2=1.42)
pgsql/contrib/tablefunc:
tablefunc.c (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tablefunc/tablefunc.c.diff?r1=1.34&r2=1.35)
pgsql/src/backend/access/transam:
xlogutils.c (r1.36 -> r1.37)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlogutils.c.diff?r1=1.36&r2=1.37)
pgsql/src/backend/commands:
prepare.c (r1.37 -> r1.38)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/prepare.c.diff?r1=1.37&r2=1.38)
pgsql/src/backend/executor:
execGrouping.c (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execGrouping.c.diff?r1=1.14&r2=1.15)
pgsql/src/backend/nodes:
tidbitmap.c (r1.3 -> r1.4)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/tidbitmap.c.diff?r1=1.3&r2=1.4)
pgsql/src/backend/postmaster:
pgstat.c (r1.94 -> r1.95)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/pgstat.c.diff?r1=1.94&r2=1.95)
pgsql/src/backend/storage/buffer:
buf_table.c (r1.40 -> r1.41)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/buf_table.c.diff?r1=1.40&r2=1.41)
localbuf.c (r1.66 -> r1.67)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/localbuf.c.diff?r1=1.66&r2=1.67)
pgsql/src/backend/storage/freespace:
freespace.c (r1.44 -> r1.45)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/freespace/freespace.c.diff?r1=1.44&r2=1.45)
pgsql/src/backend/storage/ipc:
shmem.c (r1.83 -> r1.84)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/shmem.c.diff?r1=1.83&r2=1.84)
pgsql/src/backend/storage/lmgr:
lock.c (r1.152 -> r1.153)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lock.c.diff?r1=1.152&r2=1.153)
pgsql/src/backend/storage/smgr:
md.c (r1.114 -> r1.115)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/smgr/md.c.diff?r1=1.114&r2=1.115)
smgr.c (r1.86 -> r1.87)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/smgr/smgr.c.diff?r1=1.86&r2=1.87)
pgsql/src/backend/utils/adt:
ri_triggers.c (r1.77 -> r1.78)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/ri_triggers.c.diff?r1=1.77&r2=1.78)
pgsql/src/backend/utils/cache:
relcache.c (r1.224 -> r1.225)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/relcache.c.diff?r1=1.224&r2=1.225)
typcache.c (r1.13 -> r1.14)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/typcache.c.diff?r1=1.13&r2=1.14)
pgsql/src/backend/utils/fmgr:
fmgr.c (r1.94 -> r1.95)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/fmgr/fmgr.c.diff?r1=1.94&r2=1.95)
pgsql/src/backend/utils/hash:
dynahash.c (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/hash/dynahash.c.diff?r1=1.60&r2=1.61)
pgsql/src/backend/utils/mmgr:
portalmem.c (r1.79 -> r1.80)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mmgr/portalmem.c.diff?r1=1.79&r2=1.80)
pgsql/src/include/utils:
hsearch.h (r1.35 -> r1.36)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/hsearch.h.diff?r1=1.35&r2=1.36)
pgsql/src/pl/plpgsql/src:
pl_comp.c (r1.89 -> r1.90)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_comp.c.diff?r1=1.89&r2=1.90)
pgsql/src/timezone:
pgtz.c (r1.31 -> r1.32)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/timezone/pgtz.c.diff?r1=1.31&r2=1.32)