Changed _addRecentTile to use in-place update
Changed _addRecentTile to use in-place update

An in-place update of the _recent_tiles is probably
easier on the gc. Thanks for the suggestion @juliomalegria

Billups/TileStache,TileStache/TileStache,Billups/TileStache,SEL-Columbia/TileStache,Kosta-Github/TileStache,SEL-Columbia/TileStache,Kosta-Github/TileStache,jbants/TileStache,jbants/TileStache,SEL-Columbia/TileStache,Kosta-Github/TileStache,TileStache/TileStache,Billups/TileStache,MetGIS/TileStache,MetGIS/TileStache,MetGIS/TileStache,jbants/TileStache,TileStache/TileStache