[web/facet] Use an Exists node in HasRelationFacet The generated RQL now includes an EXISTS clause. For instance, one gets: :: DISTINCT Any WHERE X is CWUser, EXISTS(X in_group A) instead of: :: DISTINCT Any WHERE X is CWUser, X in_group A for a HasRelationFacet with ``rtype = 'in_group'``, which is more appropriate for testing the existence of the relation. Add a test for this facet along the way.

/*
 * cubicweb js mock for unit tests
 * This module defines variables and functions used in quite a few places
 * in cw js framework that can't be used or guessed without a real CW server
 */

var pageid = 'my-page-id';

function _(message) {
    return message;
}