* more revision control systems
* support for tracking repo renames

  It should be possible to tell mr that there used to be a repo at
  src/foo/bar, and it's been moved to src/bar. mr would then detect if the
  move needs to be done, and handle it. This is mostly useful when mrconfig
  files are shared accross several systems.

  [src/bar]
  renamedfrom = src/foo/bar

  (Support multple renames of a single repo?)

* repo deletions

  Handling repo deletions might also be possible, but is tricky, since
  there's no good way to tell if a local checkout of a given repo is clean
  and really should be deleted. Probably better for mr to just warn that a
  repo still exists on disk that it is no longer managed.

  [src/foo/baz]
  deleted = yes

* mr register

  Idea is you check out a repo and then use mr register to add it to the
  closest mrconfig file.

  mr register would be implemented as a shell command that then calls
  mr config with flags that make it actually edit the mrconfig file:

  if [ -d "$MR_REPO/.svn" ]; then
  	url=$(svn info "$MR_REPO" | grep -i ^URL: | cut -d ' ' -f 2)
	if [ -z "$url" ]; then
		error "cannot determine svn url"
	fi
	mr -c "$MR_CONFIG" config --add "$MR_REPO" --checkout="svn co $URL"
  fi