Added code to interact with the SAML Attribute Service.
Added a test for the AttributeService client and fixed some issues.
Extra AttributeService test
Significantly simplified SAML Attribute handling.

It turns out that the ESGF AttributeService doesn't use the groupRole type any more.
Attributes are just name/value pairs so we can do away with FriendlyName and URNs.
Support attributes with multiple values
Added convenience class for deducing service endpoints
Reorganising
Added issuer parameter to AttributeService suggested by Prashanth