[ajax js/css] modconcat fix: load code exactly once (auc, fcayre) * introduces cw.ajax namespace (currently hosts only recent modconcat functionality) * handle load-one/load-many-at-once edge case * properly handle already-loaded js resource * avoid .appendTo to trigger script evaluation since from jquery 1.5 this results in uncached ajax calls

debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/etwist/ usr/lib/PY_VERSION/site-packages/cubicweb/