more strict checking on group file default=true

[https://www.google.com/accounts/o8/id?id=AItOawmQmn0B7szSWU05XNIWqq49So7cIisAOpI]

When I first set up bcfg2 a few years ago I didn't really 100% understand every entry in the group file. so when I got it working I just kept the syntax. This meant that every group profile in my config had default='true' set. when this was the case any new client checking into bcfg2 with the proper auth but no entry in my clients file would get added to the last group profile as defined in the groups file.

should probably add some sanity checking to make sure there is only one default='true' defined in the config.

[solj]

Warning added in [5831].