Issue 4005: Remove .sort() call on dict_keys object.

This caused pydoc to fail when there was a zip file in sys.path.

Patch contributed by Amaury Forgeot d'Arc.
diff --git a/Lib/pkgutil.py b/Lib/pkgutil.py
index 27dd887..0ec6ec5 100644
--- a/Lib/pkgutil.py
+++ b/Lib/pkgutil.py
@@ -318,8 +318,7 @@
     from zipimport import zipimporter
 
     def iter_zipimport_modules(importer, prefix=''):
-        dirlist = zipimport._zip_directory_cache[importer.archive].keys()
-        dirlist.sort()
+        dirlist = sorted(zipimport._zip_directory_cache[importer.archive])
         _prefix = importer.prefix
         plen = len(_prefix)
         yielded = {}