This patch implements EMACS_SOCKET_NAME in emacsclient, providing the
same sort of "set the argument from the environment" feature for the
socket name as for other features.
I use this to enable a stable, consistent path on a set of machines
where I use Unix domain socket forwarding and TRAMP to enable easy
emacsclient use from within tmux -- where I can't easily know the UID
I'll be logged in as programatically.
While this certainly could be a "you have a configuration problem", the
symmetry with other settings including the TRAMP prefix makes me feel
this is a useful addition -- or at least, not out of line with how
similar options can be configured.