Modified task initialisation so that stack now comes beneath the environment

Environment is backed by a special per-task file maintained by mm0 for each task.
This file is filled in by the env pager, by simple copying of env data into the
faulty page upon a fault. UTCB and all anon regions (stack) could use the same
scheme.

Fixed IS_ERR(x) to accept negative values that are above -1000 for errors. This
protects against false positives for pointers such as 0xE0000000.

	modified:   include/l4/generic/scheduler.h
	modified:   include/l4/macros.h
	modified:   src/arch/arm/exception.c
	modified:   tasks/fs0/include/linker.lds
	modified:   tasks/libl4/src/init.c
	modified:   tasks/libposix/shm.c
	new file:   tasks/mm0/include/env.h
	modified:   tasks/mm0/include/file.h
	new file:   tasks/mm0/include/lib/addr.h
	deleted:    tasks/mm0/include/lib/vaddr.h
	modified:   tasks/mm0/include/task.h
	new file:   tasks/mm0/include/utcb.h
	new file:   tasks/mm0/src/env.c
	modified:   tasks/mm0/src/fault.c
	modified:   tasks/mm0/src/file.c
	modified:   tasks/mm0/src/init.c
	new file:   tasks/mm0/src/lib/addr.c
	modified:   tasks/mm0/src/lib/idpool.c
	deleted:    tasks/mm0/src/lib/vaddr.c
	modified:   tasks/mm0/src/mmap.c
	modified:   tasks/mm0/src/shm.c
	modified:   tasks/mm0/src/task.c
	new file:   tasks/mm0/src/utcb.c
	modified:   tasks/test0/include/linker.lds

tasks/libposix/shm.c

@@ -11,9 +11,7 @@
 #include <l4lib/arch/syscalls.h>
 #include <l4lib/arch/syslib.h>
 #include <l4lib/ipcdefs.h>
-
-#define PTR_ERR(x)		((void *)(x))
-#define IS_ERR(x)		(((int)(x)) < 0)
+#include <l4/macros.h>
 
 int l4_shmget(l4id_t key, int size, int shmflg)
 {