workaround a cache issue refers #258

--HG--
branch : distribute
extra : rebase_source : c8897b0541098e34f4347621f54ed79ef32be229

CHANGES.txt

@@ -7,6 +7,7 @@ CHANGES
 ------
 
 * Issue #249: Added options to exclude 2to3 fixers
+* Issue #258: Workaround a cache issue
 
 ------
 0.6.23

pkg_resources.py

@@ -508,6 +508,10 @@ class WorkingSet(object):
         """
         seen = {}
         for item in self.entries:
+            if item not in self.entry_keys:
+                # workaround a cache issue
+                continue
+
             for key in self.entry_keys[item]:
                 if key not in seen:
                     seen[key]=1