skip over ID3 tags in fallback files

if we do not skip then the resync code triggers trying to find a valid frame
and if the tag is large enough then it could cause a client drop.
always have a mime types tree, and add another search function for it

the tree is now built whether the mime types file is read or it is populated by
the internal defaults.

The search function is a linear search for a matching mime type so that a filename
extension can be obtained. This is for a subsequent patch for xslt processing
added missing prototype
add header for content disposition

This is in case you have xsl files sending non-html content to browsers
fix initialisation bug in cases of no metadata requested on relays
expand on mpeg ts frame check