Kernel: Add ASSERTion to Process::exit()

This is just so I don't forget that exit can currently only
be called on the executing thread itself

kernel/kernel/Process.cpp

@@ -149,6 +149,7 @@ namespace Kernel
 		s_process_lock.unlock();
 
 		// FIXME: we can't assume this is the current process
+		ASSERT(&Process::current() == this);
 		Scheduler::get().set_current_process_done();
 	}