Correct man page dates

Various changes (many by me) have been made to the man pages without
bumping their dates. I have now corrected them based on the last commit
to each file. I also added the script I used to make these changes.

Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Laager <rlaager@wiktel.com>
Closes #8710