That link should work just fine. Just in case you don't realise it - it will not work from a browser - only from an SVN client.
In any case, z-push-2 will be stable enough for most production sites once release 2.0.3 is available (the RC is due out in 2 days and the final release is due on Sept 13) so it probably does not make sense to build out a new install based on the unofficial as12.1 branch. There will be an updated zimbra backend for z-push-2 available by then too.

