Import uses paths relative to the root of the repository, so when
user imports patch with paths relative to the current working directory
import aborts with 'unable to find file for patching'.
This patch improves this situation by warning the user that paths are
relative to the root of repository when patching fails.
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.
