bug#12399: 24.2.50; dired-do-touch doesn't recognize empty input in minibuffer

[Stefan Monnier]

> Fortunately, thanks to `completing-read-function'
> it's easy to fix this with a small change that adds
> a new function `completing-read-without-default'
> that works like `completing-read-default'
> but returns the empty string for empty input
> like `read-from-minibuffer':

There's another way to do that: check (eq val default), since the
returned value will be `eq' to the `default' if the minibuffer was
empty, whereas if it comes from a non-empty minibuffer it will at best
be `equal'.


        Stefan