Some activity registry fixes. Thanks cjb.

sugar/activity/__init__.py

@@ -36,4 +36,6 @@ class.  This class allows for querying the ID of the root
 window, requesting sharing across the network, and basic
 "what type of application are you" queries.
 """
-
+from sugar.activity.registry import ActivityRegistry
+from sugar.activity.registry import get_registry
+from sugar.activity.registry import ActivityInfo

sugar/activity/registry.py

@@ -58,7 +58,10 @@ class ActivityRegistry(object):
         info_list = self._registry.GetActivitiesForType(mime_type)
         return self._convert_info_list(info_list)
 
-_registry = ActivityRegistry()
+_registry = None
 
 def get_registry():
+    global _registry
+    if not _registry:
+        _registry = ActivityRegistry()
     return _registry