* 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

  (How to support multple renames of a single repo? List multiple
  renamedfrom dirs?)

* a way to detect repos in a tree that are not registered, and warn
  about or even auto-register them. (svn externals make this quite
  difficult!)

* When there are chained mrconfig files, mr could be smarter about
  checkouts and updates. Ie, when a new version of an mrconfig file is
  checked out or updated, throw all the info from the old one away, and
  process the new one.

  Until this is fixed, checkouts and updates need to be manually repeated
  after mrconfig files have changes.