Fix a problem with zip paths reported by Ashley Walsh.

--HG--
branch : setuptools
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/trunk/setuptools%4041173

pkg_resources.py

@@ -1122,7 +1122,7 @@ class ZipProvider(EggProvider):
             for path in self.zipinfo:
                 parts = path.split(os.sep)
                 while parts:
-                    parent = '/'.join(parts[:-1])
+                    parent = os.sep.join(parts[:-1])
                     if parent in ind:
                         ind[parent].append(parts[-1])
                         break