[GEOS-5840] Changing the default style of a layer won't cause truncation of the tile caches for layer groups containing the layer, and, [GEOS-4760] Make GWC tile layers use the GeoServer layer's http caching settings
Merge pull request #247 from aaime/fix_gwc_caching

[GEOS-5840]  and [GEOS-4760]