revert to old find_files interface

[srenatus]

Fixes #276.

Included tests are minimal.

[chris-rock]

Maybe we can simplify this:

return files if exit_status == 0
# received an error
warn "find_files(): non-zero exit status: #{exit_status}"
return []

[chris-rock]

@srenatus Thanks for the improvement of the find_files test. This is much better now. I think we can simplify the exit code handling even further.

[srenatus]

@chris-rock ok, updated (if I understood your proposal correctly). While the find_files_or_error method might seem superfluous, it conveys the intention of 1345c1d to allow the utility method user to recognize errors.

⚠️ That said, the method is still not robust, the "default" handling doesn't work; will add tests and fixes in a minute.

[chris-rock]

cool that is so simple now.

[srenatus]

Tests should be improved, but I'd rather just see this bug gone now. :)

[chris-rock]

Thanks @srenatus for this fix.