Re: chown should catch null owner:group

[jidanni]

EB> `:'
EB> ~     If only a colon is given, or if NEW-OWNER is empty, neither the
EB> ~     owner nor the group is changed.

OK, I'll drop my case, but please add a comment to this documentation
about "why" or "who knows why?" or the motivation behind or uses of,
this case.

Perhaps "just to be orthogonal".

Else people wonder what's up the sleeve.

JM> I think it makes sense to diagnose a spec of "." as invalid.

OK, you dudes take it from here. Thanks.