Improve gem loading to prevent mismatch

Ok this has bugged me long enough to improve it, this checks not only that a local dev directory exists, but that the version matches... ( **edit** as long as major and minor match, we shouldn't care about patch)

Which means it won't attempt to use 3.x against 2.99 etc which bundler won't let you do anyway. If people approve I will pick this to all the main repo's and the 3 branches.