py3: convert key to str to make kwargs.pop work in mq

The keys are passed here and there as unicodes and our transformer make things
bytes. Due to that, mq was not poped and this results in error on Py3.
Here we abuse r'' to make that str on Python 3.

hgext/mq.py

@@ -3540,7 +3540,7 b' def mqcommand(orig, ui, repo, *args, **k'
     """Add --mq option to operate on patch repository instead of main"""
 
     # some commands do not like getting unknown options
-    mq = kwargs.pop('mq', None)
+    mq = kwargs.pop(r'mq', None)
 
     if not mq:
         return orig(ui, repo, *args, **kwargs)