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.
