major enhancements to views integration. 'posts in specified group' filter and...

major enhancements to views integration. 'posts in specified group' filter and the analogous argument now accept strings like 3,4,7 and 3+4+7. like taxonomy urls, this elects posts that are in all those groups are any of those groups. also added a filter and an argument which accept substrings on group titles so you can see all nodes belonging to groups with the word 'marketing' in them. this fulfills some of the needs for subgroups.