Attached patch adds "application/xhtml+xml" mime type for *.xhtml resource files. This is the correct Mime type per http://www.w3.org/TR/xhtml-media-types/.
IE doesn't support it natively yet, but does with the help of, e.g., the MathPlayer MathML plugin, which is useful for pages with the XHTML 1.1 plus MathML 2.0 DocType.