Remove the '<->' operator

[alexcrichton]

There may be a more efficient implementation of core::util::swap_ptr. The issue mentioned using move_val_init, but I couldn't figure out what that did, so I just used copy_memory a few times instead.

I'm not exactly the best at reading LLVM generated by rust, but this does appear to be optimized away just as expected (when possible).

[thestinger]

The copy_memory function will be faster than move_val_init, which zeroes where it moves from. However, copy_memory uses the memmove intrinsic and the swap function itself (not the *mut version) could take advantage of the guarantee that &mut pointers are non-aliasing and use memcpy instead. It doesn't seem to be exposed anymore though...

[graydon]

needs a rebase

[alexcrichton]

Should be good to go again

[pcwalton]

Unfortunately this is bitrotted again :(

[alexcrichton]

Rebased for now at least, these keep creeping in...

[alexcrichton]

Well that's unfortunate, right after I pushed I wanted to make sure that the failing test from last time passed, and then I just forgot to check the output an hour later. This time the test actually passes! Perhaps the 5th time's the charm?