Translate the errno to gctl_error() texts.

Spotted by:	mwlucas


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274313 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Report the 1-based key numbers rather than the 0-based ones to be consistent.

Fix documentation for destroy command.  Not sure how the wrong explanation
happened.

Spotted by:	mwlucas


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274314 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f