Raise POSKeyError instead of KeyError in loadBefore. (#6)

This prevents a KeyError: '\x00\x00\x00\x00\x00\x00\x00\x00'

CHANGES.txt

 Changelog
 =========
 
+- Raise POSKeyError instead of KeyError in loadBefore.
+
 3.0 - 2016-04-03
 ----------------
 

src/tempstorage/TemporaryStorage.py

@@ -192,7 +192,7 @@ class TemporaryStorage(BaseStorage, ConflictResolvingStorage):
         try:
             tids = [stid for soid, stid in self._conflict_cache if soid == oid]
             if not tids:
-                raise KeyError(oid)
+                raise POSException.POSKeyError(oid)
             tids.sort()
             i = bisect.bisect_left(tids, tid) -1
             if i == -1: