patch 8.0.1817: a timer may change v:count unexpectedly

Problem:    A timer may change v:count unexpectedly.
Solution:   Save and restore v:count and similar variables when a timer
            callback is invoked. (closes #2897)
diff --git a/src/version.c b/src/version.c
index f94090f..81f867b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1817,
+/**/
     1816,
 /**/
     1815,