rewrite revert command. fix issues 93, 123, 147.
new version does these things:
- saves backup copies of modified files (issue 147)
- prints output like other commands, and errors when files not found
(issue 123)
- marks files added/removed (issue 93)
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory