Don't refilter .all() and .find() if only properties changed

Might need minor cleanup, maybe a unit test. Also would like to rename 'ready' 
@stefanpenner I think this solves sandstorm's problem and overall should lead to major perf
Yes, I think IE7 in document mode (possibly 8 too, in quirks mode) will fail[1].

[1] http://stackoverflow.com/questions/7246618/trailing-commas-in-javascript