CODE: get rid of karte_t::scroll_lock

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6840 8aca7d54-2c30-db11-9de9-000461428c89
Loading old and new savegames, even save double height games some version back

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6841 8aca7d54-2c30-db11-9de9-000461428c89
FIX: no longer accept offset outside the scroll areas

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6842 8aca7d54-2c30-db11-9de9-000461428c89