patch 8.1.0293: checks for type of stack is cryptic

Problem:    Checks for type of stack is cryptic.
Solution:   Define IS_QF_STACK() and IS_LL_STACK(). (Yegappan Lakshmanan)

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    293,
 /**/
     292,
 /**/