Let's switch to Bazaar!

We need to meet all of the WorkflowRequirements.

Here's what we need to do:

 * Install trac-bzr plugin
   * Upgrade trac to the latest version (or trunk?)
     * Upgrade all the templates to the new format
     * Update trac plugins to account for any plugin API changes
       * mailer (drop this and use the builtin mailer?)
       * irc announcements
       * user database (drop this and use the builtin account stuff?)
     * Make sure trac modifications still work
 * Replace the post-commit hooks
   * mailer
   * buildbot
   * IRC bot
   * trac integration -- we might not need this
 * Update release scripts
 * Update developer documentation
 * Change the revision-number-in-version code to handle svn
   * .bzr/branch/last-revision
 * Make a decision about what to do with Combinator
   * Ignore Combinator
   * Give it a Bazaar backend, making it just a path-mgmt system