Hopefully puts out burning tinderbox.

rustc: Remove a few allocations from metadata. Shaves a few milliseconds off compilation of hello world.

this will require more temporaries, but is probably less magical.
also, it means that borrowck matches trans better, so fewer crashes.
bonus.

Finally, stop warning about implicit copies when we are actually borrowing.

Also, one test (vec-res-add) stopped failing due to #2587, and hence I
added an xfail-test.

Fixes #3217, #2977, #3067

This commit breaks the item-printing functionality. It will return in a faster
form.

Fixing long lines.

This is so that we don't generate 170,000-line LLVM functions in Servo.

This should avoid allocation in many select paths.