Adopt C99 bool in the edsf API.

Adopt C99 bool in the edsf API.

Now the flag passed to edsf_merge to say whether two items are the
same or opposite is a bool, and so is the flag returned via a pointer
argument from edsf_canonify.

The latter requires client code to be updated to match (otherwise
you'll get a pointer type error), so I've done that update in Loopy,
which is edsf's only current in-tree client.