Add partial_min/max to libcore/cmp

Add partial_min/max to libcore/cmp

Match against None and mark as experimental

Shortened documentation.

Removed whitespace
Integrate builtin bounds fully into the trait checker
Integrate caching of results. Measurements show approx 90% hit rate.
Move unsafe destructor check from kind.rs into wf.rs
Remove checks that are already being done during typeck
Remove redundant local variable checks.
Move checks for closure bounds out of kind.rs
Remove the last redundant check from kindck, and then remove the pass as well.
Move checking of whether fields are Sized or not into wf / trait code.
Remove as much of TypeContents as I can -- unfortunately, it is still
used by EUV to compute whether a given type moves-by-default.
Fix various places that were affected by adding core as dep of libc
Fix BitvSet union_with and symmetric_difference_with giving incorrect results when the BitvSet passed in is larger than self.