Added a CPU type check during the OSX version check steps.

As I unfortunately learned yesterday at Installfest, if you run RailsInstaller on a 32-bit system, bad shit happens if the installer fails to fully install (which is frequent in 32-bit), and it's a royal pain to clean up.  Since students are not apt to know what type of CPU their running, I added in some steps to check what CPU type their running.

If their on a 32-bit machine and can't source a 64-bit machine for classes the next day, they'll probably need a volunteer to help them build the environment manually due to them probably being on an older version of OSX and needing to make sure to grab 32-bit binaries when available.  Thus the lack of instructions for students on 32-bit systems besides "flag an instructor".