updated for version 7.3.991

Problem:    More can be shared by Python 2 and 3.
Solution:   Move more stuff to if_py_both. (ZyX)

src/version.c

@@ -728,6 +728,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    991,
 /**/
     990,
 /**/