invariants.cpp tests the ACE Token Invariant utilities.  The ACE Token
Invariant utilities allow an application to test the correctness of
mutex and readers/writer locks.

invariants.cpp takes no command-line arguments.  invariants.cpp first
tests readers/writer locks.  This is done by spawning two threads
which simulate reader and writer acquire/renew/release loops.
However, the loops are performed without actual locks, so the
competing threads quickly reach and invalid state.  The test should
report this violation of readers/writer lock invariants and both
threads should exit.

The second test is for mutexes.  Similar to the readers/writer lock
test, this test spawns two threads which perform acquire/renew/release
loops.  When to two threads reach an invalid mutex state, the error
should be reported and the threads should exit.

For these two previous tests, it is theoretically possible that the
threads never reach an invalid token state.  However, it is highly
unlikely since the threads would have to execute the same code
simultaneously for the duration of the test.  Nevertheless, it is
possible.

The last test hardwires invalid token states.  It runs two mutex and
two readers/writer lock tests.  It should report "succeeded" for the
four tests.