dillon1000/react

Test case showing reassignment block scoping problem

This demonstrates a situation we don't handle well today. The basic structure is 
that you have some variable defined at the top level, then some control flow 
like if/switch where _all_ branches reassign the variable, then some code after 
that references the resulting phi node: 

```javascript 

let x1; 

// ... mutate/read x1 

if (cond) { 

x2 = {}; 

} else { 

x3 = {}; 

} 

x4 = phi(x2, x3); 

``` 

We currently group x3, x3, and x4 into a scope together, but note that...there's 
no `let` declaration for any of those! This means that it looks like the scope 
for x2 and x3 start in the consequent/alternate, but the true scope spans from 
before-after the if. I'm inclined to say that LeaveSSA should run _before_ scope 
analysis, and produce something like the following in this case: 

```javascript 

let x1; 

// ...mutate/read x1 

let x2; // new variable declaration for the new version of x 

if (cond) { 

x2 = {}; 

} else { 

x2 = {}; 

} 

x2; 

``` 

This then allows us to construct a correct range for x2, which starts in the 
other block.