patch 7.4.857

Problem:    Dragging the current tab with the mouse doesn't work properly.
Solution:   Take the current tabpage index into account. (Hirohito Higashi)

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    857,
 /**/
     856,
 /**/