This check was previously in `create` only, not applying to renames. It
should really be applied at the libbe level, so that we can avoid
writing about this restriction over and over again.
While we're here: `bectl rename` always succeeds, even when it doesn't.
Start returning the error.
Reported By: Christian McDonald <cmcdonald netgate com>
Reviewed by: rew, jwmaag_gmail.com (earlier version)
Differential Revision: https://reviews.freebsd.org/D34605
dadb9c7093