make stuff const

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6835 8aca7d54-2c30-db11-9de9-000461428c89
squelch compiler warnings

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6836 8aca7d54-2c30-db11-9de9-000461428c89
(Ters) use std::string::size_type

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6837 8aca7d54-2c30-db11-9de9-000461428c89
sqapi: export is_available

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6838 8aca7d54-2c30-db11-9de9-000461428c89
code tidy - min and max clipping for koord

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6839 8aca7d54-2c30-db11-9de9-000461428c89