patch 8.0.1352: dead URLs in the help go unnoticed

Problem:    Dead URLs in the help go unnoticed.
Solution:   Add a script to check URLs in the help files. (Christian Brabandt)
diff --git a/Filelist b/Filelist
index 12d9e00..269206f 100644
--- a/Filelist
+++ b/Filelist
@@ -584,6 +584,7 @@
 		runtime/doc/*.txt \
 		runtime/doc/Makefile \
 		runtime/doc/doctags.c \
+		runtime/doc/test_urls.vim \
 		runtime/doc/vim.1 \
 		runtime/doc/evim.1 \
 		runtime/doc/vimdiff.1 \