Mutex test progress

- Mutex test added. Forked tasks demonstrate produce/consumer using a
  shared mmap'ed page.
- Added l4lib assembler syscall
- Added forgotten SWI to mutex control offset in syscall page.
- Added mutex head initialization
- Contended child successfully sleeps in a waitqueue.

Issues:
- Somehow the child's produced page buffer is altered at about [4020] offset.
  Parent fails to validate buffer therefore.
- Need to add syncing to test so that parent does not unlock and lock again
  before child has a chance to lock buffer and produce.

src/glue/arm/init.c

@@ -26,6 +26,7 @@
 #include INC_PLAT(printascii.h)
 #include INC_API(syscall.h)
 #include INC_API(kip.h)
+#include INC_API(mutex.h)
 
 unsigned int kernel_mapping_end;
 
@@ -344,6 +345,7 @@ void init_tasks()
 	/* Initialise the global task and address space lists */
 	init_ktcb_list();
 	init_address_space_list();
+	init_mutex_queue_head();
 
 	printk("%s: Initialized. Starting %s as pager.\n",
 	       __KERNELNAME__, __PAGERNAME__);