Previously, groups with GROUP_VISIBILITY_NONE could be selected for an
availability condition, but as the group API did not return a user's own
groups with this visibility, the condition's is_available check always
failed.
This change uses the new $includehidden parameter to get all of a user's
groups from groups_get_user_groups when evaluating the condition, so
these groups work as expected. Due to the enforced hiding of conditions
containing these groups, they will never be seen by the user.
Mark Johnson
39af71da2c