Allow namedset to use vary using function about eprints3.4

[drn05r]

There is a potential for this to break or at least make the output from /cgi/schema inaccurate. I would advise that if such a function is used the default return value should be one that encompasses all possible options.

[drn05r]

This can be done by configuring the workflow as follows:

<epc:choose>
    <epc:when test="type = 'article'">
        <field ref="license" set_name="licenses_for_article"/>
     </epc:when>
     <epc:otherwise>
         <field ref="license"/>
     </epc:otherwise>
</epc:choose>

It does mean you need to define a separate set of phrases for licenses_for_article. You should probably do something like the following to make sure license typename phrases are consistent:

<epp:phrase id="licenses_for_article_typename_cc_by_nd_4" ref="licenses_typename_cc_by_nd_4"/>

You need not for the licence description phrases (e.g. licenses_for_article_description_cc_by_nd_4) as it will not know what namedset was used it will just assume the one in the field configuration, so it is important that those license description phrases are present.