Specifiy invalid chars in username error message

- Refactored list of invalid chars out to constant

app/models/user.rb

@@ -88,12 +88,17 @@ class User < ActiveRecord::Base
                     :default_url => "/assets/:class/:attachment/:style.png",
                     :styles => { :large => "100x100>", :small => "50x50>" }
 
+  INVALID_CHARS = "/;.,?%#"
+
   validates :display_name, :presence => true, :allow_nil => true, :length => 3..255,
                            :exclusion => %w[new terms save confirm confirm-email go_public reset-password forgot-password suspended]
   validates :display_name, :if => proc { |u| u.display_name_changed? },
                            :uniqueness => { :case_sensitive => false }
   validates :display_name, :if => proc { |u| u.display_name_changed? },
-                           :format => { :with => %r{\A[^\x00-\x1f\x7f\ufffe\uffff/;.,?%#]*\z} }
+                           :format => { :with => %r{\A[^\x00-\x1f\x7f\ufffe\uffff]*\z} }
+  validates :display_name, :if => proc { |u| u.display_name_changed? },
+                           :format => { :with => %r{\A[^#{INVALID_CHARS}]*\z},
+                                        :message => "cannot contain invalid chars: #{INVALID_CHARS}", invalid_chars: INVALID_CHARS }
   validates :display_name, :if => proc { |u| u.display_name_changed? },
                            :format => { :with => /\A\S/, :message => "has leading whitespace" }
   validates :display_name, :if => proc { |u| u.display_name_changed? },