rebase: use context manager for locking in rebase()

test-http-proxy: redirect proxy stdout to /dev/null This output hasn't been getting flushed, but would alter the log if it ever grew large enough. See 23b07333a8b2.

test-logtoprocess: don't run on Windows Several bits of output were missing[1], unless the DETACHED_PROCESS flag is _not_ passed to subprocess.Popen(). The problem with that is it briefly opens and closes several cmd.exe windows on screen. Foozy also mentioned some other issues in that thread. With this, the last of the long standing Windows failures fixed, the test suite now runs cleanly (536 ran, 67 skipped) on Windows 7 x64, with python 2.7.13. \o/ [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-April/096987.html

revset: add support of keyword arguments to ancestors() and descendants() Prepares for adding depth parameter.

revsetlang: check arguments passed to ancestors() before optimizing to only() Future patches will add depth parameter to ancestors(), which isn't compatible with only().

revsetlang: factor out helper to match ancestors() in parsed tree More checks will be added.

templatekw: use common "rev:node" format as the default of predecessors I'm not sure if this is better. If we're planning to add a template keyword that returns obsoleted nodes unavailable in the repo (i.e. they have no valid revision numbers), we might want to use the current "node"-only format everywhere.