Custom/more underspecification options for sortinfo

[emm68]

I modified the is_more_specific/is_less_specific methods of Sortinfo to treat a value 'tensed' of the slot 'tense' as less specific than any other value except for 'untensed'. I discussed the issue with @guyemerson and we agreed that this hacky solution is reasonable for now, but it scratches a surface of a deeper issue to be resolved in future.

Once we start tackling that, the hacky change introduced by the commit 637aa1a should be removed.