Need to determine stock info of basket lines which have attributes

If you have a product that requires options, then you sometimes need to know the value of the options (eg line attributes) to determine availability.  The current strategy object doesn't have an API for this.

Example: on the basket page, when listing a bundle product, you need to know the availability of all the subproducts to know the bundle availability.

Suggestion: extend the strategy class to have a new API for accepting a basket line, or line options so that we can handle this situation.  The template tag will also need adjusting to ensure basket lines can be rendered correctly.