Introduce new alternative PHP core library pro DH
Valid and correct version of XML sitemap generator

Done changes?
	- Remove HTML formatting from sitemaps
	- sitemaps/index.php, improved response headers recognition
	- sitemaps/sitemap-basic.xml, changed priorities in template

Note: This was orignally a cherry-pick of 6bc0622.
Merge branch 'sitemap' into dh-1.5