Proper tracking of file-level operations: rename, directories, merges

[Stephen J. Turnbull]

Barry Warsaw writes:

 > That's another interesting distinction between Mercurial and
 > Bazaar, I think.  In some sense the `bzr` command is just a thin
 > layer on top of a library, and it's the library which makes
 > guarantees about API stability.  I think that's a much more sane
 > guarantee to make.

When git and Mercurial were born, nobody had a clue about what a DVCS
UI should look like.  If the command line interface is stable, then
anybody can help evolve the UI.  If you ask people to learn a huge
library API on top of a new programming language, almost nobody will.

Also, you need to remember that scripting isn't just three-line shell
functions; it's fairly large programming systems like vc.el and magit.
You'll make a lot of people very unhappy if those stop working.  AFAIK
bzr hasn't change UI on the Emacs people yet, but I'm pretty sure
you'll hear about it if there are any UI changes that affect vc.el!