clear() needs to reset the _length attribute

lib/python/Products/PluginIndexes/DateIndex/DateIndex.py

@@ -98,7 +98,7 @@ class DateIndex(UnIndex, PropertyManager):
         """ Complete reset """
         self._index = IOBTree()
         self._unindex = OIBTree()
-
+        self._length.set(0)
 
     def index_object( self, documentId, obj, threshold=None ):
         """index an object, normalizing the indexed value to an integer

lib/python/Products/PluginIndexes/DateRangeIndex/DateRangeIndex.py

@@ -136,6 +136,7 @@ class DateRangeIndex(UnIndex):
         self._since         = IOBTree()
         self._until         = IOBTree()
         self._unindex       = IOBTree() # 'datum' will be a tuple of date ints
+        self._length.set(0)
 
     #
     #   PluggableIndexInterface implementation (XXX inherit assertions?)