CHG: merge dirty tiles into larger rectangles and process in 32bit chunks instead of bit by bit

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6511 8aca7d54-2c30-db11-9de9-000461428c89
FIX: icons update on changing player colours

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6512 8aca7d54-2c30-db11-9de9-000461428c89