More file type checks...

More file type checks...
* Switch XML type detection/validity check from dipping for XML processing instructions, doctypes, or subtags to just trying to parse it and checking the root element's name and namespace. This lets us properly handle SVG files which specify a namespace but no doctype, as well as rejecting files that aren't well-formed. (See http://meta.wikimedia.org/wiki/SVG_validity_checks for some samples of bad files I encountered.) Non-XML files will abort parsing pretty quickly, so this shouldn't be a big burden on other types that didn't hit a magic check.
* Fix Unicode unix script checks (er.... is that even right? :D), remove the iconv dependency