Added a shared memory test.

- libposix error printing now configurable via macro definition
- shmget/at/dt tested.

tasks/libposix/time.c

@@ -2,6 +2,7 @@
 #include <l4lib/arch/syscalls.h>
 #include <sys/time.h>
 #include <errno.h>
+#include <libposix.h>
 
 int gettimeofday(struct timeval *tv, struct timezone *tz)
 {