Factor MirrorUpdater out of GitRevisionWriter and move it to dvcs_common.py
Patch by: Greg Ward <greg@gerg.ca>
* cvs2svn_lib/dvcs_common.py: new class MirrorUpdater
* cvs2svn_lib/git_output_option.py:
- make GitRevisionWriter a subclass of MirrorUpdater
- remove responsibility for self._mirror from start(), finish()
- remove _mkdir_p(), process_revision()
- remove most of add_file(), modify_file(), delete_file()
- change order of args to start(); adjust GitRevisionInlineWriter
and caller
git-svn-id: http://cvs2svn.tigris.org/svn/cvs2svn/trunk@4905 be7e6eca-30d4-0310-a8e5-ac0d63af7087