bug#25183: 26.0.50; expanding quoted file name on w32

[Eli Zaretskii]

> From: npostavs@users.sourceforge.net
> Cc: michael.albinus@gmx.de,  25183@debbugs.gnu.org
> Date: Sat, 24 Dec 2016 08:57:45 -0500
> 
> If we want to extend the /: quoting to also apply to relative file names
> too, then the latter makes sense.  Otherwise, the only consistent result
> would be
> 
>     (expand-file-name "/:~/path/./file") => (error "/: quoting relative file 
> name")

expand-file-name doesn't signal errors, and I don't think it would be
a good idea to have it start doing that.

> As I've said in https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25183#29,
> currently "/:~/foo" is a kind of paradoxical file name, being
> both/neither relative nor absolute.

file-name-absolute-p is not smart enough to handle this case with the
rigor we are discussing, so I don't think this aspect is important for
the purposes of this discussion.  The "/:" quoting was chosen because
it fools file-name-absolute-p, so the above is not surprising.