Assuming the type ":touch", Collector.new was calling
send(:touch), which instead of triggering method_missing
and generating a new collector method, actually
invoked the private method `touch` inherited from
Object.
By generating the method for each mime type as it
is registered, the private methods on Object can
never be reached by `send`, because the `Collector`
will have them before `send` is called on it.
To do this, a callback mechanism was added to Mime::Type
This allows someone to add a callback for whenever
a new mime type is registered. The callback then
gets called with the new mime as a parameter.
This is then used in AbstractController::Collector
to generate new collector methods after each mime
is registered.
