type limit comparisons should be conservative with respect to `uint`

The following code:

```
            assert!(v <= 0xFFFF_FFFF_u);
```

issues a warning on a 32-bit build but not a 64-bit build (because `v` is a `uint`).  This is annoying. We should consider `uint` to be 64-bits for the purposes of this lint mode, which is inline with our general philosophy that you of segregating `uint` from `u32` and `u64` to encourage portability between 32-bit and 64-bit.
