feature request: single flag to unset ControlPath

[Tom Spindler]

While it's real handy to have "ControlMaster auto" to have multiple
sessions get muxed into one, sometimes it's really helpful to _not_
use the same session (e.g. if you want to ssh -2fNR).

It'd be quite nice if there were a flag to tell openssh to not mux
the new connection at all - i.e. what "ssh -o ControlPath=none"
does.  (The 'obvious' invocation `ssh -S /dev/null` doesn't work
unless you also specify `-o ControlMaster=no` - and that still
produces a warning about connection refused.) The ControlPath=none
bit is somewhat buried in the manpages, and somewhat annoying to
type interactively - hence this request.

"-P" seems like it might be the best choice for such a flag, as it's
related to the control Path.

If I'm reading the source correctly, all that'd be required for the
flag is to have 'options->control_oath = NULL;'.