checksum of the file in question, optionally preceeded by `0x'.
This has been tested, and does work, AFAICT. There is currently no md5 equivalent
of the '-s' flag for use with checksum.
specification, but _not_ in the file hierarchy. contrib'd by:
Ed Symanzik <zik@enoch.cl.msu.edu>. Man page adjustment to match, and
minor man page cleanup, by me.