diff xmit of animation queues. Also, StreamBuffer::unwrite_to

luprex/core/cpp/streambuffer.hpp

@@ -372,6 +372,9 @@ public:
     // Rewind the read cursor to a previous position.
     void unread_to(int64_t read_count);
     
+    // Rewind the write cursor to a previous position.
+    void unwrite_to(int64_t write_count);
+    
     // Use the stream buffer as a lua_Writer.
     static int lua_writer(lua_State *L, const void* p, size_t sz, void* ud);
     void *lua_writer_ud();