Clear member_roles table before populating it.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2729 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20090503121505_populate_member_roles.rb

@@ -1,5 +1,6 @@
 class PopulateMemberRoles < ActiveRecord::Migration
   def self.up
+    MemberRole.delete_all
     Member.find(:all).each do |member|
       MemberRole.create!(:member_id => member.id, :role_id => member.role_id)
     end