Has_many :through extended with writer and clear methods

I’ve extended the has_many :through association to include a clear
method as well as adding a mass assignment for the collection, since it
already has a working << method on edge rails.

I wanted to know if what I am doing is sane and/or if it is redundant
because it is already being worked into rails edge.

The full description and code is at

If there is a better way to handle this, or if there is some reason that
what I’m doing will cause other problems, please let me know.
Otherwise, feel free to use it.

Perhaps, I’ll submit it as a patch to the dev team if anyone else thinks
it’s useful.