When applying a patch renaming/copying 'a' to 'b' on a revision where
'a' does not exist, the patching process would abort immediately,
without processing the remaining hunks and without reporting it. This
patch makes the patching no longer abort and possible hunks applied on
the copied/renamed file be written in reject files.
_updatedir() is no longer used by internalpatch()
The change in test-mq-missingfiles.t comes from workingbackend not considering
the missing 'b' file as changed, thus not calling addremove() on it.