Capability checking added as compiling code.

Capability checking for thread_control, exregs, mutex, cap_control,
ipc, and map system calls.

The visualised model is implemented in code that compiles, but
actual functionality hasn't been tested.

Need to add:
- Dynamic assignment of initial resources matching with what's
defined in the configuration.
- A paged-thread-group, since that would be a logical group of
seperation from a capability point-of-view.
- Resource ids for various tasks. E.g.
  - Memory capabilities don't have target resources.
  - Thread capability assumes current container for THREAD_CREATE.
  - Mutex syscall assumes current thread (this one may not need
    any changing)
  - cap_control syscall assumes current thread. It may happen to
    be that another thread's capability list is manipulated.

Last but not least:
- A simple and easy-to-use userspace library for dynamic expansion
  of resource domains as new resources are created such as threads.

include/l4/generic/thread.h

@@ -11,7 +11,7 @@ void thread_id_pool_init(void);
 int thread_id_new(void);
 int thread_id_del(int tid);
 
-void task_destroy_current(void);
+void thread_destroy_current(void);
 void task_make_zombie(struct ktcb *task);
 
 #endif /* __GENERIC_THREAD_H__ */