dot/emacs: Look for running server before leaping at starting a new one.

I used to use `warning-suppress-types' to muffle this, but it doesn't
work any more because there's a new mechanism for `delayed warnings'.
If we're still starting up (and not being a daemon or noninteractive)
then warnings get put on a list to deal with later -- but the
suppression lists aren't saved, so the warning `escapes' from under my
attempt to muffle it.

Instead, look to see if there's a server already running, and just print
a message if there is.