added NotSupported Exception

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40297

scrapy/trunk/scrapy/core/exceptions.py

@@ -21,7 +21,7 @@ class IgnoreRequest(Exception):
 class DontCloseDomain(Exception):
     """Request the domain not to be closed yet"""
     pass
-    
+
 class HttpException(Exception):
     def __init__(self, status, message, response):
         if not message:
@@ -42,3 +42,6 @@ class DropItem(Exception):
     """Drop item from the item pipeline"""
     pass
 
+class NotSupported(Exception):
+    """Indicates a feature or method is not supported"""
+    pass