clients & tests: Unify multiple definitions of x*alloc and related functions

Direct fail_on_null calls now produce output like:

    [weston-info] clients/weston-info.c:714: out of memory

xmalloc, et al produce output on failure like:

    [weston-info] out of memory (-1)

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/tests/presentation-test.c b/tests/presentation-test.c
index a985c06..f8c3be5 100644
--- a/tests/presentation-test.c
+++ b/tests/presentation-test.c
@@ -32,6 +32,7 @@
 #include <time.h>
 
 #include "shared/helpers.h"
+#include "shared/xalloc.h"
 #include "weston-test-client-helper.h"
 #include "presentation-time-client-protocol.h"