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)
abort: Failed to parse .../t/.hg/hgrc
File contains no section headers.
file: .../t/.hg/hgrc, line: 1
'invalid\n'