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.

Basic install:

 $ make            # see install targets
 $ make install    # do a system-wide install
 $ hg debuginstall # sanity-check setup
 $ hg              # see help

See http://www.selenic.com/mercurial/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.