bug#31859: 26.1; Emacs has no way to determine if the current instance has a running server

[Eli Zaretskii]

> From: Thibault Polge <thibault@thb.lt>
> Date: Sat, 16 Jun 2018 18:27:03 +0200
> 
> > Does it work to test whether server-process is bound and non-nil?
> 
> It works, indeed.  Would you accept a documentation PR on the variable
> and the two functions, which are much more obvious candidates?
> Something like:
> 
> For a general way of determining if the current instance has a server
> running, check the value of `server-process`.
> 
> Or a PR adding a stupid helper function like:

I'd prefer a documentation change, but let's see if someone has other
opinions.