I'm using Subversion to access the latest SpamAssassin code.
Fair enough, then you know and understand that you're using an unstable, in-development version. A lot of the code is being freshly tested here and may not work perfectly, though it generally functions 99.9%.
config: warning: score set for non-existent rule DIGEST_MULTIPLE
*shrug* since the rules and scores are set in separate files this isn't surprising. They were probably in the process of adding or removing the rule when you checked out, or it got half-checked-in by accident. Either way, this kind of minor warning does sometimes crop up in the devel version, which should not surprise you.
Wait a day or two and check out a new SVN. Or go back to using official releases if you want something that will always work with fewer glitches, bugs and weirdness.
debug: diag: module not installed: Razor2::Client::Agent ('require' failed)
Could that be the reason for the lint complaint? I don't use Razor and I thought it was not required?
It's not required... does SA fail to run?
Note that the perl "require" statement can be used to check if something is installed, or not of a particular minimum version. I suspect that's all the above message means.