file-name-shadow-mode breaks viper-mode's // interpretation

[Jim Meyering]

Ever since around Nov 15, (which is when file-name-shadow-mode went in,
or was turned on by default), when I run emacs -q, then do M-x viper-mode,
if I try to open a file by typing C-x C-f /tmp/junk,
(e.g., I see /current/dir//tmp/junk in minibuffer) I end up
instead with a dired buffer on `.' (aka /current/dir).

If I turn off file-name-shadow-mode, everything works as usual.

So, to reproduce,

touch /tmp/junk
emacs -q -f viper-mode
[ Respond `y' to the viperize question. ]
[ Type C-x C-f /tmp/junk RET ]

You end up in a dired buffer rather than with the file you
just touched.