bug 1076873 - sitemap.xml contains empty <urlset> tag

add a link to the tree's home page as the first entry in every sitemap.  This solves two problems:
1) the home page will be added to the sitemap
2) none of the sitemaps will be empty
Merge pull request #49 from ljm42/patch-1

bug 1076873 - sitemap.xml contains empty <urlset> tag