fixup! ERP5Type: make XMLMatrix a mixin

product/ERP5Type/XMLUtils.py

 from xml.etree.ElementTree import iterparse, Element, TreeBuilder, XMLParser
-from .XMLMatrix import INFINITE_SET
+from .mixin.matrix import INFINITE_SET
 
 class RestrictedElement(Element):
   __allow_access_to_unprotected_subobjects__ = 1
@@ -79,4 +79,4 @@ def parseStream(stream, child_discard_set, callback_dict, catchall=None):
             ),
           ),
         ):
-    callback_dict.get((event, elem.tag), catchall)(elem)
\ No newline at end of file
+    callback_dict.get((event, elem.tag), catchall)(elem)