Add new function xzalloc(n) as a shorthand for xcalloc(1, n).

lib/util.c

@@ -42,6 +42,12 @@ xcalloc(size_t count, size_t size)
     return p;
 }
 
+void *
+xzalloc(size_t size)
+{
+    return xcalloc(1, size);
+}
+
 void *
 xmalloc(size_t size) 
 {