R1:2216a5e6efb9

Add Subversion ref and content logs to pre-commit hooks

Summary: Ref T4195. SVN has no such thing as refs (I was thinking about writing a quasi-ref anyway like `HEAD: r23 -> r24`, but I'm not sure it would actually be useful). And content is very easy to build.

Test Plan: Pushed some stuff to SVN, got logs from it.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4195

Differential Revision: https://secure.phabricator.com/D7766