Make sure existing custom fields visibility is set to true.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4383 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20101107130441_add_custom_fields_visible.rb

 class AddCustomFieldsVisible < ActiveRecord::Migration
   def self.up
     add_column :custom_fields, :visible, :boolean, :null => false, :default => true
+    CustomField.update_all("visible = #{CustomField.connection.quoted_true}")
   end
 
   def self.down