Make Makefile more compatible

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7319 8aca7d54-2c30-db11-9de9-000461428c89
ADD: signal handler to gracefully terminate a server

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7320 8aca7d54-2c30-db11-9de9-000461428c89
CHG: hinding soft keyboard on mobile devices is optional

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7321 8aca7d54-2c30-db11-9de9-000461428c89