[process] Add DBG2() messages to help track down frozen processes

src/core/process.c

 	list_for_each_entry ( process, &run_queue, list ) {
 		list_del ( &process->list );
 		list_add_tail ( &process->list, &run_queue );
+		DBGC2 ( process, "PROCESS %p executing\n", process );
 		process->step ( process );
+		DBGC2 ( process, "PROCESS %p finished executing\n", process );
 		break;
 	}
 }