Add mutex lock in memheap object.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2366 bbd45198-f89e-11dd-88c7-29a3b14d5316

include/rtdef.h

@@ -595,6 +595,8 @@ struct rt_memheap
 
     struct rt_memheap_item *free_list;                  /**< free block list */
     struct rt_memheap_item  free_header;                /**< free block list header */
+
+	struct rt_mutex         lock;                       /**< mutex lock */
 };
 
 /**