Fix handling of boolean attributes

My schema has an object class with a required boolean value.

Now, when I pass the Ruby false (FalseClass) to the attribute of the ActiveLdap-object, then the new value is not transferred to the server and validation fails.

Here I have a patch that will solve the problem. The main-problem is, that `false.blank?` will evaulate to `true`. Thus `false` is handled like an empty string. IMHO this is wrong. What`s your opinion?

Please can you review the patch? Any comments?

Bye, Robin.