fastannotate: adapt to buffer() going a way in Python 3

There's probably something more efficient I could do here, but I'm disinclined
to spend much time on this at the moment.

Differential Revision: https://phab.mercurial-scm.org/D5614

hgext/fastannotate/protocol.py

@@ -101,7 +101,7 b' def _parseresponse(payload):'
         ch = payload[i:i + 1]
         if ch == '\0':
             if state == 1:
-                result[vfspath] = buffer(payload, i + 1, int(size))
+                result[vfspath] = payload[i + 1:i + 1 + int(size)]
                 i += int(size)
                 state = 0
                 vfspath = size = ''