fix Py3k compiler crash due to new importlib

Cython/Utils.py

@@ -50,11 +50,13 @@ def path_exists(path):
     # figure out if a PEP 302 loader is around
     try:
         loader = __loader__
-        # XXX the code below assumes as 'zipimport.zipimporter' instance
+        # XXX the code below assumes a 'zipimport.zipimporter' instance
         # XXX should be easy to generalize, but too lazy right now to write it
-        if path.startswith(loader.archive):
-            nrmpath = os.path.normpath(path)
-            arcname = nrmpath[len(loader.archive)+1:]
+        archive_path = getattr(loader, 'archive', None)
+        if archive_path:
+            normpath = os.path.normpath(path)
+            if normpath.startswith(archive_path):
+                arcname = normpath[len(archive_path)+1:]
                 try:
                     loader.get_data(arcname)
                     return True