SECURITY: Remove email validation check bypass

- Increase size of email column to varchar(513)
 - Give error message on signup when email is too large

Overall impact: Low, allows signups from blocked domains. Main risk is increased spam.

db/migrate/20150713203955_enlarge_users_email_field.rb

@@ -0,0 +1,8 @@
+class EnlargeUsersEmailField < ActiveRecord::Migration
+  def up
+    change_column :users, :email, :string, :limit => 513
+  end
+  def down
+    change_column :users, :email, :string, :limit => 128
+  end
+end