Stefan Monnier wrote:

> Hmm... is it really Emacs that displayed it like this?  Or is it the
> terminal which did it?  If it's Emacs, then I wonder how it figured it
> needed to do that

I haven't looked at the details, but I expect Emacs looks at the locale and 
discovers that it's unibyte.  At least, that's how I did it: by starting xterm 
in an Ubuntu 15.04 environment where LC_ALL=en_US.iso885915, and then running 
emacs -nw under xterm.  In this situation, the attached patch to Emacs (which 
would have to be improved before installing) has the behavior of using 
underlined ` and ' to render curved single quotes.