FIX: compile with no display

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7279 8aca7d54-2c30-db11-9de9-000461428c89
FIX: crash during city street building

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7280 8aca7d54-2c30-db11-9de9-000461428c89
FIX: city road building checks to see whether levelled tile has been flooded

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7281 8aca7d54-2c30-db11-9de9-000461428c89
FIX: sliced underground mode now shows slopes rising up to current level

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7282 8aca7d54-2c30-db11-9de9-000461428c89
FIX: no crash when AI uses flatten tool and land floods

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7283 8aca7d54-2c30-db11-9de9-000461428c89
Merge pull request #2 from aburch/master

[Nightly@7283] Push latest nightly changes to Simutrans for iOS build.