Portray `Clause' on the current output stream. Layout of the
clause is to our best standards. As the actual variable names
are not available we use A, B, ... Deals with ';', '|', '->' and
calls via meta-call predicates as determined using the predicate
property meta_predicate. If Clause contains attributed
variables, these are treated as normal variables.
If Options is provided, the option-list is passed to
write_term/3 that does the final writing of arguments.