dillon1000/react

TryStatement: handle edge case control flows

Adds handling for some cases where the handler is unreachable (or is provably 
unreachable after analysis & optimization), where the try/catch can be flattened 
away: 

* The try block is empty. Nothing can throw, so the handler is unreachable. 

* The try block will always return. It can't return anything interesting (ie the 
result of a function call or variable load) since those could throw, but a try 
block that always return a primitive means the handler is unreachable. 

* The same, except where we only determine that the try block always returns via 
constant propagation.