Remove an XXX by explaining the try/except/pass.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1654 71dcc9de-d417-0410-9af5-da40c76e7ee4

neo/storage/transactions.py

@@ -208,7 +208,8 @@ class TransactionManager(object):
             try:
                 del self._load_lock_dict[oid]
             except KeyError:
-                # XXX: explain why
+                # The transaction may have not been lock when abort is called,
+                # so no read lock can be held
                 pass
             del self._store_lock_dict[oid]
         # _uuid_dict entry will be deleted at node disconnection