FLUID-5271: Corrected closure strategy in framework to enable successful use in uPortal

Test cases now check for many cases of inadvertent leakage of global "fluid" back into closures. Correction of onModelChange event signature which was an unnecessary breakage from Infusion 1.4 which also caused trouble to uPortal integration.

@michelled - could you look at this today since it is required urgently by the uPortal team? Thanks!