Only set mode of new patch if the target file was removed before.
If the file is writable by the user, but owned by a different user, the
chmod will otherwise fail with "Operation not permitted".
Additionally make very sure that the file is only written if either the number
of links is <= 1 or the file was successfully removed.
Maybe this minimal COW code should be replaced by something from util.
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
pulling from ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
(run 'hg update' to get a working copy)
1 files updated, 0 files merged, 1 files removed, 0 files unresolved