- added read / write lock support
- added non-fatal error support to allow use of mutex in fatal error reporting pathway
- isolated pthread implementation to it own header/cpp file pair
- expanded unit tests to cover new code as well as better test existing mutex
- removed a layer of complexity that added no real value
If the thread starts slowly enough it will succeed in taking the lock,
leading to a deadlock. We saw this test hanging on some of our bots
inside of pthread's lock acquire.
