Add a missing SpyAgency mixin for the SVN test cases.
Add a missing SpyAgency mixin for the SVN test cases.

This was added locally, but didn't make it into the resulting change.
This adds the SpyAgency so that spy_on will work for faking log data.

brennie/reviewboard,brennie/reviewboard,bkochendorfer/reviewboard,KnowNo/reviewboard,chipx86/reviewboard,chipx86/reviewboard,KnowNo/reviewboard,sgallagher/reviewboard,reviewboard/reviewboard,beol/reviewboard,sgallagher/reviewboard,bkochendorfer/reviewboard,reviewboard/reviewboard,davidt/reviewboard,davidt/reviewboard,bkochendorfer/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard,reviewboard/reviewboard,beol/reviewboard,beol/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,bkochendorfer/reviewboard,brennie/reviewboard,KnowNo/reviewboard,KnowNo/reviewboard,davidt/reviewboard,brennie/reviewboard,beol/reviewboard,davidt/reviewboard