Tools only accept --help, except as a first argument.
Maybe this is a long standing tradition, but at first glance I couldn't find
that it was a "wontfix" problem (perhaps for its amusement value?).
[pryzbyj(at)sentinel-centos6 ~]$ vacuumdb -a --help
vacuumdb: unrecognized option '--help'
Try "vacuumdb --help" for more information.
[pryzbyj(at)sentinel-centos6 ~]$ vacuumdb --help -a 2>&1 |sed q
vacuumdb cleans and analyzes a PostgreSQL database.
[pryzbyj(at)sentinel-centos6 ~]$ vacuumdb -V
vacuumdb (PostgreSQL) 9.6beta3