On SBCL, improve print-object reference-condition in logical blocks in src/conditions.lisp

* src/conditions.lisp (print-object :after reference-condition): on
  SBCL, act differently depending on whether the stream is a pretty
  printing stream
* test/conditions.lisp (test reference-condition.print/logical-block):
  new test; test printing `reference-condition' within a logical block