Make safe-condition-message a bit safer.

CCL ignores *print-cirlce* when *print-pretty* is t
so it's easy to run into endless recursions.

* slime-tests.el (report-condition-with-circular-list): Use
with-standard-io-syntax to override settings from init files that
any reasonable person would have.

* swank-backend.lisp (print-condition): Replaces
format-sldb-condition.  Take a stream as argument so that we can
pass in our stream with limited output length.  No guarantee of
course that this stream will be used in a reasonable way.
* swank-clisp.lisp (format-sldb-condition): Deleted. Whitespace is
now removed anyway.
* swank-sbcl.lisp (print-condition): Use the stream argument.

* swank.lisp (%condition-message): Renamed from
condition-message. Trim whitespace from the result.
(%%condition-message): New function. Use with-string-stream.
Since the length of the string is limited we can also limit
*print-length* without losing anything. Also handle
SERIOUS-CONDITIONs instead of ERRORs, which would have handled
CCL's VECTOR-SIZE-LIMITATION condition during printing.
(safe-condition-message): Just call
*sldb-condition-printer*. People who set that will know what
they're doing.
ChangeLog entry