New helper run_and_cmp to automate the job: run a program capturing
its standard output, standard error and exit status, then compare the
actual with the expected results.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
The other test output files have fixed names, and having just one with
a name that varies with the test name complicates things with no gain.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
