Type tracking array elements

[Bablakeluke]

Whilst Nitrassic is generally good at tracking types, it currently struggles with arrays primarily due to this use case:

`
var arr=[]; // Must know it's an array of numbers

function pusher(a){
a.push(1);
}

pusher(arr);
`

The information that the array contains numbers needs to backtrack out of the function. Backtracking type information is required in a few other instances too and it does appear that a general purpose solution is possible.

Asm.js emits the above form of code regularly, so it's important that it is supported. At the moment it will compile, but attempting to manipulate the array afterwards will result in exceptions as most dynamic resolving is currently disabled (in order to make sure types are preserved as often as is possible).