Attribute filter

[Rod Widdowson]

> Are you suggesting merging the RequestedAttribute case with the mapped
> EntityAttribute case and just doing one function? Otherwise I don't know
> what you mean.

I'm proposing adding a *new* MatchFunctorType to the schema.  This behaves
towards EntityAttributes in the same way as [Requested]AttributeInMetadata
does towards RequestedAttributes.  I am not suggesting making any changes to
the 99% case for EntityAttributes (EntityAttributeExactMatch and
EntityAttributeRegexpMatch).

The code is merged into one class because at one stage I thought this was
where we had to go.  At configuration time we inject a Function to say
whether to get the mapped attributes from the ACS metadata
([Requested]AttributeInMetadata) or from the EntityDescriptor metadata
(EntityAttributeInMetadata). 

The test configurations in idp-config/src/test/resources/mapping show how I
envisage that this new functor might be used.

/Rod