py3: implement __bytes__ for committablectx Before this method, calling bytes on workingctx or memctx calls basectx.__bytes__ since the magic method was not defined for this class. When it calls the method from basectx class, it returns TypeError because None is passed into it. After this commit `hg update -C` works on Python 3 if eol is not enabled.

--- a/mercurial/context.py	Fri Jun 02 10:35:21 2017 +0530
+++ b/mercurial/context.py	Thu Jun 01 02:25:18 2017 +0530
@@ -1405,6 +1405,9 @@
     def __str__(self):
         return str(self._parents[0]) + r"+"
 
+    def __bytes__(self):
+        return bytes(self._parents[0]) + "+"
+
     def __nonzero__(self):
         return True