[WIP] Some preloader refactoring

I'm refactoring our preloader changes to get the code to be more similar to the Rails preloader.  This should help us to port our preloader changes to 4.2 and eventually upstream.
Totally agree.  I have no problem with killing 1.9, I just remember you wanted to sort of "support" it for as long as possible (can't remember why...maybe so devs didn't have to upgrade to 2.0 until they really needed it to?).  If you are good, then let's lock down the Ruby version in the Gemfile.