Inline the fifo_q functions to speed them up and silence compiler warnings
for unused API calls.  Add a fifo_q_full call to hide the details of that.
Alloc work queues along with the async_nif at the end of that memory block.
Fix a few places where things should be free'd and were not.  Change enqueue
to return 0 when shutting down.  Fix a race related to shutdown.  When I use
gdb eunit calls ?cmd() seem to fail, so I've created rmdir:path() to replace
?cmd("rm -rf path") calls.