handle non-recursive path search in the ATRelativePathCriterionConverter

[dest81]

Now ATRelativePathCriterionConverter says 'Cannot handle non-recursive path search ....'

class ATRelativePathCriterionConverter(CriterionConverter):
    # We also have path.isWithinRelative, but its function is not defined.
    operator_code = 'string.relativePath'

    def get_query_value(self, value, index, criterion):
        if not criterion.Recurse():
            logger.warn(
                'Cannot handle non-recursive path search. '
                'Allowing recursive search. %r',
                value,
            )
        return criterion.getRelativePath()

In the plone.app.querystring we see that depth value can be passed as ::x.

Will send PR.