Added a "Member of Role" to the issues filters. #5869

This filter will check an issue's assigned to field for users who have
(or don't have) a specific Role(s).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4078 e93f8b46-1217-0410-a6f0-8f06a7374b81