accept headers

We discussed the accept headers issue that came up at the WG telecon, at 
the Jena meeting today.

In Jena the accept header we currently try to use is:

Accept: application/rdf+xml,application/xml;q=0.9,*/*;q=0.5
Accept-Charset: utf-8,*


issues include:

- N3, Ntriple mime types are not well-defined
- web servers are not necessarily set up correctly

- older parts of Jena may not use the new code path

Any advice would be welcome

Jeremy