emacsclient: create a new frame if one doesn't exist

[Eddie Hillenbrand]

I'm using emacsclient with emacs --daemon, but I find myself wanting a
different behavior than the standard options provide.

It would be nice if emacsclient could create a window system frame
only when one doesn't exist and if one does exist simply reuse that
frame.

I know I can get this behavior by initially invoking emacsclient with
-c and then subsequently invoking it without the -c, however I'd
prefer not to think about whether I need to include the -c when
opening files.

Thankfully there is the --eval option. I wrote some Elisp that can be
passed to emacsclient to provide this behavior, but it occurred to me
that it may be general enough to include in emacsclient as a standard
option.

I'm proposing adding a -C option that would "create a new frame if one
doesn't exist otherwise use the current Emacs frame." I'd be happy to
make the required changes and submit a patch. Is this general enough
to be implemented?