For issue pypa#57 pip wrongly selects a macosx binary .zip file

Instead of a source file it downloads a binary macosx .zip file
which contains a binary installer.

pip/index.py

@@ -294,6 +294,11 @@ def _link_package_versions(self, link, search_name):
                     logger.debug('Skipping link %s; unknown archive format: %s' % (link, ext))
                     self.logged_links.add(link)
                 return []
+            if "macosx10" in link.path and ext in ('.zip'):
+                if link not in self.logged_links:
+                    logger.debug('Skipping link %s; macosx10 one' % (link))
+                    self.logged_links.add(link)
+                return []
         version = self._egg_info_matches(egg_info, search_name, link)
         if version is None:
             logger.debug('Skipping link %s; wrong project name (not %s)' % (link, search_name))