WIthout these, update_membership() will nuke existing members, group
members, and external members if they're not referenced in the parent
code. Ope.

* Refactor MCommGroup.fetch(), mainly to reduce nesting.

* Centralize defaulting of list attrs to []; the old code was both
  overly duplicated and failed to account for some situations.

* Most LDAP attributes are not case sensitive, but we were doing a
  case-sensitive check for the umichGroup object class.

* Group display name matching was only casefolding one side of the
  comparison.

This reverts merge request !4

* Refactor MCommGroup.fetch(), mainly to reduce nesting.

* Centralize defaulting of list attrs to []; the old code was both
  overly duplicated and failed to account for some situations.

* Most LDAP attributes are not case sensitive, but we were doing a
  case-sensitive check for the umichGroup object class.

* Group display name matching was only casefolding one side of the
  comparison.

empty

- group_data['members']
- group_data['memberGroups']
- group_data['expandedMembers']

* Also fix (intermittent?) issue with reserving group names with
* (.) and (_)

/profile/dn endpoint will work for uniqnames too, but return
a gross result.