Add valid gamemodes 'OSRIC', 'Killshot', 'Darwins_World_2' and 'Gaslight'; Add ALLOWDUPES to prettylst

git-svn-id: svn+ssh://svn.code.sf.net/p/pcgen/code/Trunk@22352 ef53c05b-3124-4d59-ae7d-fe3273f42be7