pg_verify_checksums: rename -d to --verbose

pg_verify_checksums: rename -d to --verbose

Using -d is odd, because we normally reserve that for a database
argument, so rename it to -v and add long version --verbose.

Also, reduce it to emit one line per file checked rather than one line
per block.

Per a complaint from Michael Banck.

Author: Yugo Nagata <[email protected]>
Reviewed-by: Michael Banck <[email protected]>
Discussion: https://postgr.es/m/20180827113411[email protected]