[development] One-to-one tables considered harmful

[Karthik]

> Dries comments that 4 modules (other than comment.module) utilize
> node_comment_statistics table:
>
> node.module
> forum.module
> tracker.module
> search.module
>
> node.module has dependencies on comment.module that I think are wrong.
> tracker.module and forum.module both depend upon comment.module already
> search.module -- not sure what's up with that.

search.module: It comes from a doxygen comment for do_search(). The
only real culprit is node.module.