Comment 1 for bug 508292

Actually, this seems entirely sufficient:

=== modified file 'lib/lp/buildmaster/model/buildfarmjob.py'
--- lib/lp/buildmaster/model/buildfarmjob.py 2010-01-16 05:54:16 +0000
+++ lib/lp/buildmaster/model/buildfarmjob.py 2010-01-16 07:43:15 +0000
@@ -19,8 +19,7 @@
 class BuildFarmJob:
     """Mix-in class for `IBuildFarmJob` implementations."""
     implements(IBuildFarmJob)
- classProvides(IBuildFarmCandidateJobSelection)
- classProvides(ISpecificBuildFarmJobClass)
+ classProvides(IBuildFarmCandidateJobSelection, ISpecificBuildFarmJobClass)

     def score(self):
         """See `IBuildFarmJob`."""