Syntax: one or more filenames separated by space
Set the filename assumed for directory URLs. The default is
"index.html" and "index.htm". This filename will be removed from stored URLs
to prevent redundant fetches of the page. So the URLs
"http://www.example.com/fun/" and
"http://www.example.com/fun/index.html" will be considered the
same and only be fetched once (as http://www.example.com/fun/).
Note that Index Name filenames are not stripped from canonical URLs
within pages (as specified via <link rel="canonical"/>