Issue: COERCE-INCOMPLETE (Version 3)

[Glenn S. Burke <gsb@ALDERAAN.SCRC.Symbolics.COM>]

I believe that any change to the status quo is incomplete without
providing a coercion mechanism whose "viewpoint" is that of a sequence.
That is effectively what the current COERCE is, overloaded with those
types which do not conflict with SEQUENCE.

Because of the problem of differing viewpoints, I'm inclined to think
that COERCE should be shrunk down to only being a sequence coercion
function, and all other coercions should be handled by the appropriate
functions.