repository: split capabilities methods into separate interface So we can implement them without having to implement support for every command. Differential Revision: https://phab.mercurial-scm.org/D3255

httppeer: implement ipeerconnection This is low hanging fruit. We might as well start somewhere. Differential Revision: https://phab.mercurial-scm.org/D3254

py3: whitelist another six passing tests Differential Revision: https://phab.mercurial-scm.org/D3286

py3: whitelist another nine passing tests Differential Revision: https://phab.mercurial-scm.org/D3253

hgweb: use our forked wsgiheaders module instead of stdlib one Now we use bytes for headers, rather than native strings. Differential Revision: https://phab.mercurial-scm.org/D2854

wsgiheaders: import a bytes-ified fork of wsgiref.headers from cpython@46f5072 This will let us restore Python 3 compatibility for tests that do http things. Differential Revision: https://phab.mercurial-scm.org/D3245

export: enable formatter support (API) This change is basically the same as "hg cat". A formatter object is created by caller. .. api:: ``cmdutil.export()`` takes a formatter as an argument.

export: extract function to write patch to file object (API) This is common use case of cmdutil.export(), and we wouldn't want to handle formatter thingy everywhere. .. api:: The ``fp`` argument is removed from ``cmdutil.export()``. Use ``cmdutil.exportfile()`` instead.

export: port _exportsingle() to formatter Pass 'fm' instead of 'write', and use fm.plain(), fm.write(), etc. instead. The callers will be updated later.

export: serialize revisions to be exported per destination file Prepares for porting to the formatter API, where we can't simply append to existing files because JSON can't be streamed for example. The modemap hack is removed since cmdutil.export() was the only user. I also made the destination filename printed only once.