Added before_destroy filter to the commentable model

[xredo]

There was a problem when deleting the commentable model. The :dependent => :destroy clause tries to destroy all comments leading to an error because each comment also destroys its child comments, resulting in the commentable model trying to destroy an unexisting child comment.

The solution is to replace the :dependent => :destroy clause for a before_destroy filter only afecting the root comments:

ruby

before_destroy { |record| record.root_comments.destroy_all }

I experienced this malfunction with _awesome_nested_set (2.1.5)_

[troex]

Thanks for the solution! I like this one more than another #32

Please merge!

[elight]

Would you mind adding a test for it? Would be glad to merge then.

[elight]

Thanks!

[xredo]

You're welcome! It's always a pleasure to collaborate. Great gem by the way ;)