GeoRSS layer - add link target propery

[Turban]

The default behavior of OpenLayers.Layer.GeoRSS is to open links shown in marker popups in a new browser window (target="_blank"). This seems to be hardcoded GeoRSS.js (line 203):  http://trac.openlayers.org/browser/trunk/openlayers/lib/OpenLayers/Layer/GeoRSS.js

This behavior is annoying, especially if the link leads to a page on the same site.

It would be better to add link target as a property OpenLayers.Layer.GeoRSS. The default value could still be "_blank" to ensure backward compatibility.