BINFO_OFFSET

[Richard Kenner]

Sometimes it's passed to ssize_binop, meaning that it is supposed to
be of type ssizeype, but something it's passed to size_binop, meaning that
it's supposed to be sizetype.  Which is correct?

We really should document it someplace when a field in the tree is required
to be of a specific type.

I'm looking at all calls to size_binop and it appears there are whole bunch
of typing errors in the cp directory: I want to have size_binop abort if
it is called with invalid types of operands.