In order to make the output zip file reproducible (independent of the
underlying filesystem's directory traversal order), sort each list of
subdirectories and each list of files before adding them to the zip
file.

(Note that we want to sort the dirs list in place, causing os.walk to
traverse the subdirectories in order.)

In order to make the output zip file reproducible (independent of the
underlying filesystem's directory traversal order), sort each list of
subdirectories and each list of files while we are generating the
RECORD file.

(Note that we want to sort the dirs list in place, causing os.walk to
traverse the subdirectories in order.)

If the wheel metadata files are physically located at the end of the
zip file, this allows other tools to modify the metadata without
rewriting the entire archive.