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/clients/resizor.c b/clients/resizor.c
index d205eb6..ad3b71b 100644
--- a/clients/resizor.c
+++ b/clients/resizor.c
@@ -35,6 +35,7 @@
 #include <wayland-client.h>
 
 #include "window.h"
+#include "shared/xalloc.h"
 
 struct spring {
 	double current;