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.

unbundle: extract checkheads in its own function We are going to refactor the unbundle function to have it working on a local repository too. Having this function extracted will ease the process. In the case of non-matching heads, the function now directly raises an exception. The top level of the function is catching it.

phase: apply publishing enforcement for "serve" source When a changegroup is added by a push on a publishing server, we ensure they are added as public. This is used to enforce publishing on server when the client is not aware of phases. It also prevents race conditions where a reader could see the changesets as draft before they get turned public by the client. Finally, this save rounds trip as the client does not need additional request to turn them public. However, this logic was only enforced when the changegroup was from a "push" source. And "push" is used for local pushes only. Wireprotocol push uses "serve" as source since Mercurial 1.9. We now enforce this logic for both "push" and "serve" sources. One could note that this logic was mainly useful during wireprotocol exchanges. So this code is finally put into good use, 9 versions after its introduction.

merge with stable