FIX: gui windows store convoihandle_t; cleanup

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6373 8aca7d54-2c30-db11-9de9-000461428c89
FIX: restore sticky/rollup state of windows again

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6374 8aca7d54-2c30-db11-9de9-000461428c89
change to release candidate 112.2, step up savegame version

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6375 8aca7d54-2c30-db11-9de9-000461428c89