some CLI commands accept "--verbose", other don't

[zooko]

For example, I can run:

tahoe cp --verbose …

and it works, but then when I run

tahoe mkdir --verbose …

it says:

tahoe:  option --verbose not recognized

For consistency, perhaps all commands should accept --verbose even if some of them (currently) don't change their behavior in the presence of it.

[zooko]

(Or actually even better would be to make all commands change their behavior to emit progress indicators and other useful tidbits when --verbose.)