Update to fix issue when using ExecutorService instances inside of the B...

Update to fix issue when using ExecutorService instances inside of the BroadcasterConfig which are not based on ThreadPoolExecutor.  The BroadcasterConfig & Broadcaster program to the ExecutorService interface (allowing components like Spring's ExecutorServiceAdapter to be injected).  However, the AtmosphereFramework#info() method performed casts to ThreadPoolExecutor to print diagnostic information which was causing a ClassCastException.