patch 8.2.1510: using "var" in :def function may refer to legacy script var

Problem:    Using "var" in a :def function may refer to a legacy Vim script
            variable.
Solution:   Require using "s:" to refer to a legacy Vim script variable.
            (closes #6771)
diff --git a/src/version.c b/src/version.c
index 1cdd69a..60726ab 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1510,
+/**/
     1509,
 /**/
     1508,