* Provide release.sh to prepare for package releases

* Compare commit timestamps in release.sh

* Preserve execute permission when preparing release

* Warn about uncommitted files when creating release

* Run git commands inside package directory in release.sh

* Avoid changing release strings in NEWS with release.sh

* Update date in DESCRIPTION with release.sh

* Handle BSD or GNU syntax for date command

* Use git author date when comparing timestamps on files

* Hide output from test of date command