OS.File already only supports UTF-8 paths on non-Windows systems, so this change
makes our different ways of accessing file paths consistent with each other.
This should prevent unexpected crashes in glibc that expect UTF-8.
This resolves#1772.
Since these are just interpreted comments, there's 0 impact on actual code.
This removes all lines that match /* vim: set(.*)tw=80: */ with S&R -- there are
a few others scattered around which will be removed manually in a second part.