(S_N_C) FIX: net wealth was not consistent after buying vehicles

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6528 8aca7d54-2c30-db11-9de9-000461428c89
Preparation for new GUI element

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6529 8aca7d54-2c30-db11-9de9-000461428c89