convert-repo improvements

[Matt Mackall]

There are a bunch of improvements in convert-repo. Chief among them is
an experimental CVS importer. It uses cvsps to find changesets. It
talks directly to 'cvs server' on localhost or over rsh/ssh. It has
full support for importing branches and tags. To use it, simply run:

 convert-repo my-project

This shows off a couple other improvements:

 - the source type is autodetected
 - the destination is automatically chosen if not supplied
   (my-project-hg)
 - a destination repo is automatically created if it doesn't exist
 - the mapfile is automatically named and created if not supplied

We can also now ask convert-repo to attempt to sort by date with a
--datesort flag.

-- 
Mathematics is the supreme nostalgia of our time.