block exception clauses not "parallel"

[cgay]

I think this is a bug in block:

block ()
  signal(make(<simple-error>))
exception (e :: <simple-error>)
  format-out("<simple-error> clause\n");
  // I think that the exception clause below should not be in effect when signal is called here.
  signal(e)
exception (e :: <error>)
  format-out("<error> clause\n");
end;
// output is:
// <simple-error> clause
// <error> clause

From the DRM:

  // https://opendylan.org/books/drm/Statement_Macros#IX-2062
  //
  // DRM: "Note that when the expressions in an exception body are executed, all handlers
  // established by the block are no longer active."
  //
  // DRM: "All exception clauses are executed in the same dynamic environment. None of
  // the handlers established in the block are visible during the execution of one of the
  // handlers. This can be thought of as parallel installation of the handlers."

So to be clear, I think the output just just be "<simple-error> clause" and it should get an unhandled exception.

Run it in the playground here: https://play.opendylan.org/shared/f8e882a15e63415b