Varinit

[panagosg7]

[Addresses issue #24]

Allowing a phi variables to be uninitialized when joining environments.

In case of an uninitialized loop phi variable, e.g.

var i;
var sum = 0; 
while (n > 0) {
  i = n;
  sum += i;
}
return sum;

The "invariant" T_i type for i will be: number + undefined.

Types need to be aligned (ziptype) when subtyping the "base" type (before loop) and "step" type (after loop body) against T_i.

[ranjitjhala]

Wow -- amazing!! that was super fast, thanks @panagosg7 !!! (Since there was quite a bit of changes in the while code, am assuming tests pass?)

[ranjitjhala]

all tests pass. merging.