Fixed bug in the in_group? method of the LdapConnect class.  This method was incorrectly returning true for non-existent groups.
adding failing test case that exhibits bug reported in #132
Merge branch 'master' of git://github.com/riverock/devise_ldap_authenticatable into in-group-fix
fixing treament of required_groups array

it has been broken in master (but not broken in 0.6.1) and we didn't
catch it until the new test i added for #132 (0f43a30).