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
The idea was that some folks, running in a trusted environment (e.g. automated testing), may prefer to show the stack traces for convenience, but others, running in production, would rather not for security reasons. Personally, I couldn't care less either way.