Fix ownership permissions when doing a rezpost

The problem addressed here was initially reported as issue #434.

Currently, a rezpost always sets the leash permissions
to COMMAND_OWNER, meaning if anyone but an owner rezposts
a submissive, then that person cannot subsequently
unleash the submissive. (Only the primary owner can unleash them.)
This commit sets the permissions in a rezpost scenario the
same as they would be in any other leashing.

There are other ways to implement this. I went with this because it modified as little code as I could manage.