This fixes a bug when multiple path criterions are used and adds an option to not search subfolders.

This fixes https://dev.plone.org/ticket/13251 and https://dev.plone.org/ticket/13123. This pull requests adds an additional "relative path criterion" that lists only items in the relative path location without listing items in subfolders (this used to be the default behavior in old collections). Adding a "search subfolder" option to each path criterion is pretty hard to do because of the internal i/o/v structure of p.a.querystring. This fix is related to another pull request on p.a.collection: https://github.com/plone/plone.app.collection/pull/10