dillon1000/react

Separate mode to validate preserving manual memoization

Adds a new mode which validates that existing manual memoization is preserved 
_without_ using information from the manual memoization to affect compilation. 
This gives us a way to try out the more aggressive version of Forget — ignoring 
manual memoization — first and see how much code bails out and what patterns 
cause this. 

We can then proceed to enable the mode to actually _preserve_ existing memo 
guarantees only where necessary.