updated for version 7.4.268

Problem:    Using exists() on a funcref for a script-local function does not
            work.
Solution:   Translate <SNR> to the special byte sequence.  Add a test.

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    268,
 /**/
     267,
 /**/