comm-files: add script to compare the list of files in two dirs

Compare the files within two directories, but not the contents of said files.
Dumps the file lists for each with 'find', sorts, then uses 'comm' to compare,
with a bit of sed to retain the full paths.

Signed-off-by: Christopher Larson <kergoth@gmail.com>
comm-files: use a pager for the output by default

Signed-off-by: Christopher Larson <kergoth@gmail.com>