fixed callstack tracker for multithreaded apps

fixed callstack tracker for multithreaded apps

made the tracker thread local, so it adheres to the particular thread and keeps the stack right.
added tests for callstack tracker in the mutex test, since it already had lots of cool thread activity.
the stack tests invoke our macro, which checks the trace's validity; there's no specific other test
of the callstack tracker in test_mutex, but the current approach will add tests to the overall count
and also complain about any errors that occur.