patch 9.0.0318: clearing screen causes flicker

Problem:    Clearing screen causes flicker.
Solution:   Do not clear but redraw in more cases.  Add () to "wait_return".

src/misc1.c

@@ -616,7 +616,7 @@ ask_yesno(char_u *str, int direct)
 
     while (r != 'y' && r != 'n')
     {
-	// same highlighting as for wait_return
+	// same highlighting as for wait_return()
 	smsg_attr(HL_ATTR(HLF_R), "%s (y/n)?", str);
 	if (direct)
 	    r = get_keystroke();