pgsql: Skip searching for subxact locks at commit.

Skip searching for subxact locks at commit.
At commit all standby locks are released
for the top-level transaction, so searching
for locks for each subtransaction is both
pointless and costly (N^2) in the presence
of many AccessExclusiveLocks.

Branch
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/31541778b612fd59257a2bf571229f400d35ecf0

Modified Files
--------------
src/backend/access/transam/xact.c |    6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)