update: replace workingctx.dirty and raising Abort by cmdutil.bailifchanged This patch makes wrapping "commands.update()" by largefiles extension useless, because "cmdutil.bailifchanged()" can detect changes of largefiles in the working directory. This patch also changes test-update-branches.t, because "cmdutil.bailifchanged()" shows more detailed information about dirty-ness of the working directory than "workingctx.dirty()".

cmdutil: allow bailifchanged to ignore merging in progress In "commands.update()", "cmdutil.bailifchanged()" isn't used for "abort if the working directory is dirty", because it forcibly examines about merging in progress. "workingctx.dirty()" used in "commands.update()" can't detect changes of largefiles in the working directory without "repo.lfstatus = True" wrapping. This is only reason of "commands.update()" wrapping by largefiles extension. On the other hand, "cmdutil.bailifchanged()" already wrapped by largefiles extension can detect changes of largefiles. This patch is a preparations for replacing "workingctx.dirty()" and raising Abort in "commands.update()" by "cmdutil.bailifchanged()". It can remove redundant "commands.update()" wrapping.

subrepo: add bailifchanged to centralize raising Abort if subrepo is dirty This patch also centralizes composing dirty reason message like "uncommitted changes in subrepository 'xxxx'".