In `servlet-respond', the server defaults to Content-Type "text/html;
charset=UTF-8" for extensions that don't appear in
`mime-type-from-extension'. This meant that CSS files, JavaScript
files, and various types of image files were getting the wrong
Content-Type, which was fine when they were served directly, but
caused clients to close the connection when they were loaded over
HTTP/1.1, which can deliver back-to-back resources on the same
connection.
Sort the types in the `mime-type-from-extension' list now that it is
longer. It's still not long enough for the order to be material for
performance.