Don't use the git describe --dirty option to append the suffix
because it only considers changes in tracked files as dirt. If
the script wants to consider untracked files as dirt then this
will not do.
Full --help usage message
Better error handling and reporting
Only considers tags that look like version numbers
Does not create and delete local "START" tag
Lots of options, including --ignore-untracked and --unmodified
Suitable for use in Batphone repository
