Expose RepositoryRuntimeException from the kernel module instead of RepositoryException

Far from perfect, but getting closer. At least all the resource-like models are sanitized.

https://www.pivotaltracker.com/story/show/78860776
? 

Because we're still in an intermediate stage of supporting both RepositoryException and RepositoryRuntimeException, the fallback strategy of both should probably be the same, no?