bug#9972: 24.0.90; "C-s/C-r" from the minibuffer don't clear the current text

[Drew Adams]

> >> IMO, It isn't worth making C-s (and C-r, C-M-s, C-M-r) 
> >> look up also in the current minibuffer text, because
> >> it is usually small enough not to need that (how often
> >> do you use that feature?).
> >
> > I use this feature all the time!
> 
> For searching in the _current_ minibuffer text?  How long are 
> such text?

1. Yes, for searching the _current_ minibuffer text.  That's what C-s/C-r are
for: searching the current buffer.

2. And yes, minibuffer text can be large - as large as you like.

The fact that it often is not large with vanilla emacs (-Q) means only that
vanilla Emacs does not offer what is needed to really take advantage of large
input.  It even still binds `SPC' and `?' to completion (except for file names)
and help!

Vanilla Emacs unnecessarily puts obstacles in the way of editing large portions
of text in the minibuffer.  That will change (slowly) with time, I have
confidence.  It took decades to get Emacs Dev to finally allow `SPC' to be
self-inserting for file-name input.

3. And if you retrieve a previous minibuffer input, or if you cycle current
candidates into the minibuffer, and you want to edit that input, then yes,
Isearch (even regexp Isearch) can be very useful.

And the larger the previous input or current candidate, the more useful Isearch
becomes.

FWIW, in Icicles it is not unusual to have large, multi-line candidates in the
minibuffer.  This includes region text, function definitions, search contexts -
what have you.

4. The minibuffer is an _editing_ buffer, among other things.  General editing
commands, including Isearch, should be available there.

5. If you want a history-search command, then use M-s/M-r.  If those do not do
what you want, then propose additional *history*-search commands and
corresponding keys.  But please do not propose to change what C-s/C-r do.  What
they do is useful, and they are the standard keys for what they do.