bdiff: Fix bogus NULL return

bdiff: dynamically allocate hunks Make the hunk list a singly-linked list rather than a large array.

merge with stable

subrepo: lazily update git's local tracking branches This continues the strategy of separation between hg pull and hg update in git subrepos by only dealing with git's branches on an update. This behavior tries to cover the bare essentials of the semantics of git pull in the subrepo when the parent repo does hg pull and hg update.

subrepo: return both mapping directions from gitbranchmap

subrepo: strip gitcommand output