patch 8.0.1466: older GTK versions don't have gtk_entry_get_text_length()

Problem:    Older GTK versions don't have gtk_entry_get_text_length().
Solution:   Add a function with #ifdefs to take care of GTK version
            differences. (Kazunobu Kuriyama, closes #2605)
diff --git a/src/version.c b/src/version.c
index 352d491..bac652b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1466,
+/**/
     1465,
 /**/
     1464,