bug#14147: 24.3.50; turn on `minibuffer-depth-indicator-mode' by default

[Drew Adams]

> > when there is a recursive minibuffer it is essential that
> > that fact be communicated to users, one way or another.
> > This mode provides one way.
> 
> It is communicated, by default: it signals an error.

That's your answer?

Why not turn on `minibuffer-depth-indicator-mode' by default?  That's the
question, not whether you signal that there is a recursive minibuffer.

Or if that's really your answer then why not also signal an error whenever there
is a recursive edit, instead of showing `[...]' in the minibuffer?

(To be clear, FWIW, this is not for me or anyone who uses my code.  Icicle mode
has always turned on `minibuffer-depth-indicator-mode'.)