add xasprintf() for upcoming changes.

calmwm.h

@@ -492,6 +492,9 @@ void			 u_spawn(char *);
 void			*xcalloc(size_t, size_t);
 void			*xmalloc(size_t);
 char			*xstrdup(const char *);
+int			 xasprintf(char **, const char *, ...)
+			    __attribute__((__format__ (printf, 2, 3)))
+			    __attribute__((__nonnull__ (2)));
 
 /* Externs */
 extern Display				*X_Dpy;

xmalloc.c

@@ -69,3 +69,19 @@ xstrdup(const char *str)
 
 	return (p);
 }
+
+int
+xasprintf(char **ret, const char *fmt, ...)
+{
+	va_list	 ap;
+	int	 i;
+
+	va_start(ap, fmt);
+	i = vasprintf(ret, fmt, ap);
+	va_end(ap);
+
+	if (i < 0 || *ret == NULL)
+		err(1, "asprintf");
+
+	return (i);
+}