[Patch #1618455 by Ben Maurer] Improve speed of HMAC by using str.translate()    instead of a more general XOR that has to construct a list.
[Patch #1618455 by Ben Maurer] Improve speed of HMAC by using str.translate()
   instead of a more general XOR that has to construct a list.

Slightly modified from Maurer's patch: the _strxor() function is no longer
necessary at all.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator