Mantis is our bug tracker. So, no, you don't download Mantis.
SVN is where developers keep/code/corroborate on the latest pre-release code.
You have access to SVN, but, it sounds as though you might want to wait for the next release.
I don't know when that will be.
(And, even though it's in _our_ bug tracker, we wish to make clear, Garry broke our MOTD not working, we just found a way around it)