645 is the unofficial update created by Anon21.
Wait, what?
r635 is (not now) the latest SVN repository code of the official version. My unofficial update is based on that version.
The SVN repository now is up to revision 637. In the near future I'll probably be patching my patch to include the changes made in 636 / 637. Hopefully the more sensible of the changes I've made will gradually be introduced into the official version (because It's going to be difficult to keep track of stuff if the devs start doing a lot of work on the official version).