Actually working soulution to issue #845
Ignore "html" files without doctype in sitemap

Files such as alexa-verify, google-site-verification, etc. Generated
files all have doctype declerations, and they are required for
standards mode in browsers.

Use real_path directly instead of recreating it as filepath.
Changelog
trailing whitespace
.htm is possible too
Merge pull request #864 from getnikola/sitemap-fixes

Sitemap fixes