py3: ensure that we don't concat bytes and str and the end result is bytes

Here obj.__module__ and obj.__name__ are str. Either we can convert them to
bytes or use an r'' and convert back to bytes when concat is done. I preferred
the later one since we are encoding only once here.

mercurial/hook.py

@@ -31,7 +31,7 b' def _pythonhook(ui, repo, htype, hname, '
 
     if callable(funcname):
         obj = funcname
-        funcname = obj.__module__ + "." + obj.__name__
+        funcname = pycompat.sysbytes(obj.__module__ + r"." + obj.__name__)
     else:
         d = funcname.rfind('.')
         if d == -1: