Ok, it's time we got JRuby's FFI and the FFI gem on the same page, so we can share updates.

Currently a large number of files we have in common with the FFI gem are not up-to-date. There are many more type configs in the gem and I'm sure there's fixes and tweaks on the JRuby side that have not been propagated to the gem.

I'll start a PR and we can get this stuff synced up. Once we match, I'd like to get the ffi "java" gem populated with the shared files so we can preinstall it and allow users to update it between JRuby releases (which is not possible right now).

cc @larskanis @ahorek @olleolleolle @eregon