How to manually set the Content-Type

Hi,

Somehow Zope doesn't always guess the correct ContentType and so it
happens that in our System we do have many 'application/x-octet-stream'
instead of 'application/pdf'.
I managed now to display the right icon by reading the first four bytes
of the file (if they read '%PDF' it's a pdf-file).
But as this method is a rather elaborate one I would want to set the
'content_type' - property manually so that this method is only called
once.
How can I accomplish this? 

regards,




Wolfgang Huber
Informationsmanagement, Anwendersysteme
Web Engineer

Johannes Kepler Universität
Altenbergerstraße 69
4040 Linz, Österreich
Tel: +43 732 2468 8082
http://www.im.jku.at