merge: report all files in _checkunknown When doing hg up, if there is a file conflict with untracked files, currently only the first such conflict is reported. With this patch, all of them are listed. With this patch error message is now reported as a: untracked file differs b: untracked file differs abort: untracked files in working directory conflict with files in requested revision instead of abort: untracked file in working directory differs from file in requested revision: 'a' This is a follow up to an old attempt to do this here: http://selenic.com/pipermail/mercurial-devel/2011-August/033625.html