Try to preserve timestamps. Fix ChangeLog generation.
* admin/update-archive.sh: Don't change timestamp on packages that have the
same md5.
* admin/archive-contents.el (batch-prepare-packages): New function.
(archive--simple-package-p): Ignore ChangeLog as well. Signal errors if the
file does not have the expected structure.
(archive--process-simple-package): Add the ChangeLog's content.
(archive--make-changelog): Only modify the file if the content changes.
(archive--process-multi-file-package): Don't make the ChangeLog here, since we
may not even have the Bzr metadata at hand any more.
* Makefile (archive-tmp): Preserve symlinks.
(process-archive): Call new batch-prepare-packages.
* .bzrignore: Add Changelog and .changelog-witness.