[OGSA-AUTHZ] comments for Use of SAML to Retrieve Authorization Credentials

I have summarized in a wiki page the comments and answers received on 'Use of SAML to Retrieve Authorization Credentials' https://forge.gridforum.org/sf/wiki/do/viewPage/projects.ogsa-authz/wiki/Ans... If everything is ok I'll do the integration and upload a new draft. Valerio