Add support for posixGroup.
Fix filter tests expectations.
Remove unused filter matching.

The member attribute presence is superfluous and it break integration with servers that don't have activated NIS schemas by default.
Merge branch 'master' into support_posix_groups

* master:
  Verify membership when the dn is in the direct list of members for a group.
Do not set `ignore_server_capabilities`.

Some server don't like this at all.
Add default search_domains to the connection.
Expose an uid reader.
Add PosixGroup classes.

Allow simple groups with members in `memberUid`.
Allow combined groups with members under subgroups defined by `member` and `uniqueMember`.
Make sure we load the group object properly when checking by user memberships.
Merge branch 'master' into support_posix_groups

* master:
  Run tests on Ruby 2.1 and not in Ruby 2.0
  Release version 1.1.5
Make sure PosixGroup#members returns an empty array when there are no `memberUid`.
Make sure PosixGroup#members return all the user entries for every `memberUid`.
Merge pull request #23 from github/support_posix_groups

Add support for posixGroup.