RFE: easier access to Subject in attribute scripts

Some users wanted to access the Subject in an attribute script.
Currently, in idp v3.2, this can be done with:

profileContext.getSubcontext("net.shibboleth.idp.authn.context.SubjectContext").getSubjects().get(0)

Scott sugested that it can be made simpler. His comments in the users list:

(...) file a RFE so we get something cleaner added to the scripting contexts. I think if we'd realized so many people wanted to dig into the subject we would have exposed something simpler. No reason we can't expose the subject alongside the principal name.