Change my mind about account name policy.

Change my mind about account name policy.

I think the leading @ is only for @mentioning people, and it's only
out of the Mastodon context that people put it on by habit as a hint
that they're talking about the fediverse.

Also, I think I prefer my account names fully qualified, so now I have
access to the correct instance domain, I'll put it in From lines where
the server didn't send one at all.