remove math dependency in viewport

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6822 8aca7d54-2c30-db11-9de9-000461428c89
ADD: ctrl modifies change water height behaviour - raise doesn't flood land at new water height, lower only drains shallow water

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6823 8aca7d54-2c30-db11-9de9-000461428c89