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/api/cap.c

@@ -110,6 +110,13 @@ int sys_capability_control(unsigned int req, unsigned int flags, void *userbuf)
 {
 	int err;
 
+	/*
+	 * Check capability to do a capability operation.
+	 * Supported only on current's caps for time being.
+	 */
+	if ((err = cap_cap_check(current, req, flags)) < 0)
+		return err;
+
 	switch(req) {
 	/* Return number of capabilities the thread has */
 	case CAP_CONTROL_NCAPS: