Update imports.py to work properly with celery_http_gateway.

Without this fix in place the following error was emitted

when trying to query a task status via the celery_http_gateway:

"sequence item 0: expected string, module found"

Traceback: http://pastie.org/4188542

celery/utils/imports.py

@@ -34,7 +34,7 @@ else:
         if not hasattr(obj, '__name__') and hasattr(obj, '__class__'):
             return qualname(obj.__class__)
 
-        return '.'.join([obj.__module__, obj.__name__])
+        return '.'.join([str(obj.__module__), str(obj.__name__)])
 
 
 def symbol_by_name(name, aliases={}, imp=None, package=None,