patch 7.4.1660
Problem:    has('patch-7.4.1') doesn't work.
Solution:   Fix off-by-one error. (Thinca)
diff --git a/src/version.c b/src/version.c
index dccdb90..1bd90fa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -749,6 +749,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1660,
+/**/
     1659,
 /**/
     1658,