arguments: the input-field *and* the binding value (not only the
binding value)
Rational: (a) transformers of non-multi input-fields can now access the
attribute field of the input-field record, (b) there is no real reason
why to treat multi and non-multi input-fields differently in respect
to their transformer arguments (keep design simple).
Updates of current surflets only necessary if they create their own
non-multi input-fields (with make-input-field). Example surlfets
calculate.scm and calculate-cb.scm updated as well as standard HTML
input-fields provided by the SUrflets.
interp