SpinLock.TryEnter fail fast for timeout 0

[benaadams]

Passes corefx tests

1M iters (single thread, uncontended but locked) for code

bool lockTaken = false;
var s = new SpinLock(false);
s.Enter(ref lockTaken);

method	pre (ms)	post (ms)	improvement
s.TryEnter(0, ref lockTaken)	24.55	6.09	x 4.0

Need to do the threadpool timing tests I have (on a couple environments), as TrySteal uses this path; and they introduce parallel contention. Hopefully will improve, but will see.

Also corrected some strange spellings.

[stephentoub]

Nit: missing comma after "If timeout is zero"

[benaadams]

Closing for now while I work through the flow a bit more.