Simplistic 'fix' for bundle import saving bug

If you attempt to save a bundle without the 'product' registry entry set
to the instance of the bundle, the associated selections objects fail to
save do to a reference to the product via the registry. This is the exact
situation you run into when importing via DataFlow.

There is probably a much better fix for this problem, but this one is
enough to make importing updates via DataFlow work.

Looking at the Magento2 code it seems they have a website_id attached to
the selection object being saved. Perhaps further research will show this
to always be the case in Magento1 as well and we could instead use that
method.