Don't cast HANDLE to usize and back

[CraftSpider]

Not sure if there's interest for this one - I'm aware of argument whether HANDLE really needs to be a pointer, and it's defined as isize for non-std mode bindgen, but it was an easy change so I figured I'd put it up for review.

[workingjubilee]

weird, code that treats pointers as pointers instead of a funny integer is actually simpler than code that treats it as a funny integer!

[ChrisDenton]

The trouble there was using two or three different definitions of HANDLE in the same code. I can only assume it was written before we had AtomicPtr otherwise I don't understand why that wasn't used in the first place.