py3: decode prompt string before calling rawinput

Calling input() (aka pycompat.rawinput() on python3) with a byte string
displays a byte string in the console. E.g. in interactive commit, we
get: b"examine changes to '<file>'?\n(enter ? for help) [Ynesfdaq?]".
Similarly, "hg email" prompts are messed up.

We thus decode the prompt string before running rawinput().

mercurial/ui.py

@@ -1555,6 +1555,7 b' class ui(object):'
         # - http://bugs.python.org/issue12833
         with self.timeblockedsection(b'stdio'):
             if usereadline:
+                prompt = encoding.strfromlocal(prompt)
                 line = encoding.strtolocal(pycompat.rawinput(prompt))
                 # When stdin is in binary mode on Windows, it can cause
                 # raw_input() to emit an extra trailing carriage return