TODO

* For compatability, ~/.mrtrust has to exist before trust checks are
  enabled. Change this in a flag day.

* After the mtrust flag day, consider making something similar to -p 
  be enabled by default. 

  It should not be identical to -p, for the following reason: -p causes
  mr to only look at the mrconfig it finds in the path (like -c only looks
  at the specified file). But by default, mr should certianly load the
  ~/.mrconfig (and files it chains). This allows a user to globally
  configure mr with aliases, etc. (Closes: #557963)

* more revision control systems

* 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. (See #447553)