Merge branch 'jn/post-receive-utf8'

Update post-receive-email script to make sure the message contents
and pathnames are encoded consistently in UTF-8.

* jn/post-receive-utf8:
  hooks/post-receive-email: set declared encoding to utf-8
  hooks/post-receive-email: force log messages in UTF-8
  hooks/post-receive-email: use plumbing instead of git log/show