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.

src/arch/arm/exception.c

@@ -113,7 +113,7 @@ void fault_ipc_to_pager(u32 faulty_pc, u32 fsr, u32 far)
 	if (current->tid == current->pagerid) {
 		printk("Pager (%d) faulted on itself. FAR: 0x%x, PC: 0x%x Exiting.\n",
 		       current->tid, fault->far, fault->faulty_pc);
-		task_destroy_current();
+		thread_destroy_current();
 	}
 
 	/* Send ipc to the task's pager */