D5698: wireprotov2peer: rewrite character traversal to use slices

[Yuya Nishihara]

+  mercurial/wireprotov2peer.py:307:
+   >                 self._ui.debug(_('received %r\n') % frame)
+   don't mark debug messages for translation
+  mercurial/wireprotov2peer.py:513:
+   >     return [True if raw[i:i+1] == b'1' else False for i in range(len(raw))]
+   missing whitespace in expression