is DAV:getcontenttype read only?

The spec (13.5) does not say whether the DAV:getcontenttype property is
readonly or not.  In mod_dav it is, in PyDAV it is not.

I claim it should not be read-only, as the client (who stored the resource
via PUT) has better knowledge of the server (which can, at best, be relying
on resource name heuristics to guess the content type).