run-tests: replace open-coded .decode()s on paths with a helper (issue4667) This also cleans up the mkdtemp code mentioned in the previous patch. At this point, the remaining callsites of .{en,de)code() are in the following categories: Handling escaped lines in .t files ----------------------------------- It seems eminently reasonable to me for us to declare that .t files are valid utf-8, and that any escape sequences we see in .t files should be valid unicode_escape sequences. Making error text safe for cdata blocks for xml error reports ------------------------------------------------------------- This is a point where we're already basically screwed, and we're simply trying to do something "good enough" that the xml output will be vaguely useful to the user. Punting here seems fine, and we should probably stick to the same encoding here that we used in the previous section.