Add Subversion support and standardize source path separators

ScmInfoPluginProjectSpec assumes the source path components will be separated by /, which does not hold on Windows.  I left the test alone and translated the source path coming from the ScmProvider instead.

I added Subversion support, including an untested hook for the [Jenkins Subversion plugin](https://wiki.jenkins-ci.org/display/JENKINS/Subversion+Plugin).
I wouldn't have noticed it at all except that on my first pass, I referenced svnkit 1.7.  Regardless, I think pretending we support the version then allowing the exception to be thrown is the right move.  Otherwise if the version isn't supported (or perhaps the repository is corrupted), it would just silently fall back to unknown, which would be a nasty surprise.  I'll update the pull request later today.