patch 8.0.0697: recorded key sequences may become invalid

Problem:    Recorded key sequences may become invalid.
Solution:   Add back KE_SNIFF removed in 7.4.1433. Use fixed numbers for the
            key_extra enum.
diff --git a/src/version.c b/src/version.c
index ebf8b8b..bd09de5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    697,
+/**/
     696,
 /**/
     695,