Allow registering a WP_List_Table class when registering post types

[sanchothefat]

This would go a long way towards making the post types feature more complete. I discovered while converting Links from the native format into a post type that the admin lists are still very clunky to work with, especially with quick edit obliterating non-underscored post meta and the quick edit form not being configurable enough on the server-side to make it useful for more unusual post type requirements.

Code-wise it would be good to work with it in a similar way to the Walker_Nav_Menu class eg. so I could extend the WP_Posts_List class to overwrite certain elements for my post type.

The list table API will be made public (and therefore extensible) for WP 3.2.

Not sure about the parameter for register_post_type() though.

Punting to future for now.