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/api/ipc.h

@@ -12,6 +12,17 @@
 
 #if defined (__KERNEL__)
 
+/*
+ * ipc syscall uses an ipc_type variable and send/recv
+ * details are embedded in this variable.
+ */
+enum IPC_TYPE {
+	IPC_INVALID = 0,
+	IPC_SEND = 1,
+	IPC_RECV = 2,
+	IPC_SENDRECV = 3,
+};
+
 /* These are for internally created ipc paths. */
 int ipc_send(l4id_t to, unsigned int flags);
 int ipc_sendrecv(l4id_t to, l4id_t from, unsigned int flags);