Semaphore files for shutting down ProBoard

It is possible to shut down ProBoard by creating a semaphore file in the ProBoard system directory. The file should be called:

DOWN.<node#> (node# is the node number)

When ProBoard finds this file, it will hang up and immediately exit with errorlevel 100. It will then create a file called ISDOWN.<node#> in the same directory to indicate that ProBoard has been shut down successfully.