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/terminal.c b/clients/terminal.c
index 7406f50..a70fef3 100644
--- a/clients/terminal.c
+++ b/clients/terminal.c
@@ -45,6 +45,7 @@
 
 #include "shared/config-parser.h"
 #include "shared/helpers.h"
+#include "shared/xalloc.h"
 #include "window.h"
 
 static int option_fullscreen;