When /bin/ed is not present the test failed with a confusing "unhandled
error".
* Wrap the whole run-program-ed test into with-test, renaming it to run-program-/bin/ed.
* Add before it a test named :is-/bin/ed-installed?.
Making the report more self-describing:
Failure: run-program.impure.lisp / IS-/BIN/ED-INSTALLED?
Failure: run-program.impure.lisp / RUN-PROGRAM-/BIN/ED