Double moves out of arrays are allowed

[zwarich]

This program is accepted, but it shouldn't be:

fn f(mut a: [Box<int>, ..2]) {
    drop(a[0]);
    a[1] = box 2;
    drop(a[0]);
}

fn main() {
    f([box 0, box 1]);
}

The problem is that array paths do not incorporate the index, and thus do not refer to a unique location, unlike other LoanPaths. Strong updates to kill previous moves are only valid for paths that refer to a unique location.