Don't use a dynamic string for wait debugging.

Happens in release, and shows up on the profiler.
Not huge, but should save ~0.5% of cpu time.
Get rid of waitTypeStrings and resched reason copy.
Cut thread switching time down.

Based on profiling release Windows.

Took these funcs from taking 1.6% to 0.5% time.
Skip a double map lookup.

Profiler says this was taking extra time.  Only saves 0.23%.
Merge pull request #507 from unknownbrackets/perf

Minor performance improvements