async/async.py:  Fixed an issue with memoization in `AsyncRunner.call()` where it wasn't working properly with functions that took no arguments.
core/server.py:  Added `CPU_ASYNC.call()` with a meaningless function to the top of the script to test that it works.  This should correct the situation on certain FreeBSD systems where Gate One would fail to start up due to there not being enough semaphores available for multiprocessing to work (reported in issue #303 - https://github.com/liftoff/GateOne/issues/303).