Use Scala reflection api instead of scalap (2.11)

This is the 2.11-requiring version of https://github.com/wg/jacks/pull/23. It has JacksMapper use TypeTags instead of Manifests and does not require jacks-managed locking for reflection. Due to the fact that it adds a hard dependency on Scala 2.11, I'd expect that this can't become the only branch for jacks, but I'd think that there's an outside possibility that you want to have this version and the one from https://github.com/wg/jacks/pull/23 (or your current scalap-based version) evolve in parallel.