Refactored the arguments object so it doesn't dictate closure layout
Created attachment 164459 [details]
Oliver asked if it's common for websites to capture arguments by name and use the arguments object at the same time. There seems to one idiom where it is common: by-hand implementation of function.bind.
I don't believe I've made this case worse than it is today, since this case reifies the arguments object to pass it to slice, etc., which disables our optimizations. Also, I don't believe this patch is incompatible with optimization, if we first eliminated the reification.
Committed r128832: <http://trac.webkit.org/changeset/128832>