Update vidcontrol -c to support all cursor appearance setting
capabilities.

Most of the capabilities (all of the arcane ones) were in FreeBSD-2.0.5,
but were harder to use then, and vidcontrol didn't try. FreeBSD-4.1.0
added per-vty support, fixed the destructivness of the "destructive"
cursor, and improved APIs. Start using the new APIs, support all of
their capabilities, and document all of the capabilities and some of
the historical mistakes.

vt doesn't support any of this before or after the change.

Fix minor unrelated bitrot in the usage message for the syscons case.