weakref fix ans implement tohash && isEqual

The weakref fix is probably similar to another pull req, but I could not figure out how to back that out. I've been using this with RM 2.5/2.6 and has been working great.

The hash/isEqual methods were implemented to fix #146. Basically, KVO blocks were not getting called correctly. It was not getting called because the @targets hash stores a formotion Row as a key. In my app (which is a pretty involved app), the calling @targets[target] would not return the proper value. Implementing hash/isEqual fixed this