py3: use bytes instead of str in isinstance()

We deal with bytes internally and things should be bytes

Differential Revision: https://phab.mercurial-scm.org/D3215

hgext/mq.py

@@ -677,7 +677,7 b' class queue(object):'
             write = self.ui.warn
 
         if all_patches or self.ui.verbose:
-            if isinstance(idx, str):
+            if isinstance(idx, bytes):
                 idx = self.series.index(idx)
             pushable, why = self.pushable(idx)
             if all_patches and pushable: