Lost socket for detached Emacs, how to regain control?

[Ulrich Mueller]

Consider the following scenario:
  - emacs --daemon is running in the background without any open frame
  - server-start is also called in another Emacs process

Now there is no more way to connect to the detached Emacs. (Or am I
missing something?)

Maybe it would be feasible to add a recovery mechanism for such a
case, like binding [sigusr1] to server-start?

Ulrich