Fix a bug in the SVN parser which causes it to find commit refs in other SVN repositories

Summary:
This query isn't scoped correctly to the repository ID, so we may identify
commits from other repositories.

This causes a somewhat subtle issue since we only use it to manage file
copies/moves, so you end up with a file "copied from" the same revision in
another repository. I think the UI probably even renders correctly.

Once I finish T325 and better understand what's going on here, I'll see how much
work is involved in writing an SQL patch to fix this.

Test Plan: Parsed the test repo from T325 with the expected error.

Reviewers: jungejason, nh, tuomaspelkonen, aran

Reviewed By: jungejason

CC: aran, jungejason

Differential Revision: 891