doc: Add 'checkman' tool

doc: Add 'checkman' tool

Add the 'checkman' script, which compares a command's "-help" output
to the options actually documented in its manpage. This command is
certainly not perfect, and may contain false negatives and false
positives. It is not (currently) intended to be run as an automated
check, but is meant to assist a human manually checking the
correctness of man pages. An error reported by 'checkman' does not
necessarily indicate something that should actually be changed.

Change-Id: Iae1965c441279dd3f93c1a7283ea0a0140d5ebe3
Reviewed-on: http://gerrit.openafs.org/10442
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>