put it back for compatibility reasons

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@2263 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Tool/Category.py

+from Products.ERP5.Document.Category import Category as ERP5Category
+from Products.ERP5.Document.BaseCategory import BaseCategory as ERP5BaseCategory
+
+class Category(ERP5Category):
+  pass
+
+class BaseCategory(ERP5BaseCategory):
+  pass