Ignore a file called modindex.html.
diff --git a/Doc/html/.cvsignore b/Doc/html/.cvsignore
index c527166..601a914 100644
--- a/Doc/html/.cvsignore
+++ b/Doc/html/.cvsignore
@@ -5,4 +5,5 @@
 mac
 ref
 tut
+modindex.html
 @webchecker.pickle