exchange: fix pyflakes import complaint

hgweb: override the charset attribute in the http request The default http request character set is UTF-8. If the message is not encoded in UTF-8, such as big5, it cannot be shown correctly. The 'charset' is overridden by the root document's, such that the user can select the proper encoding in the browser.

diff: use second filename for --stat reporting on git patches (issue4221)

exchange: drop useless line break

subrepo: check return code for git push (issue4223)

localrepo: add unbundle support Localrepo now supports the unbundle method of pushing changegroups. We plan to use the unbundle call for bundle2 so it is important that all peers supports it. The `peer.unbundle` and `peer.addchangegroup` code path have small difference so cause some test output changes. None of those changes seems problematic.

unbundle: extract the core logic in another function The `exchange` module now contains an `unbundle` function that holds the core unbundle logic. The wire protocol keeps its own unbundle function. It enforces wireprotocol-specific logic and then calls the extracted function. This aims at implementing unbundle for localrepo.