Fix incorrect variable reference.
Closes #6
Thanks @pitchandtone
Merge pull request #7 from Innovatif/master

Thanks!
Silverstripe 3 compatibility - deprecated function calls fixes
Deal with scenario where attribute is empty string
More flexible group matching, now also by ID and group object in addition to group code
Updated readme compatibility info
Allow group membership removal by calling with ID, Code or group object
Fix to stop authentication result string showing up on login form.
indendation fix
Method comments
CHANGELOG update
Merge pull request #9 from svandragt/ss3-compatibility

Ss3 compatibility - thanks @svandragt