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

[Juri Linkov]

> Try this from "emacs -Q":
> 1. Type "C-x C-f".
> 2. Type "C-s" (or "C-r").
>
> In step #2, the minibuffer prompt changes from "Find file" to
> "I-search", but the buffer's default directory is not cleared.
> Instead, it becomes read-only like the prompt text, so that I have to
> type the Isearch input after it.
>
> This is quite confusing.  The minibuffer should be cleared, like "M-s"
> and "M-r" commands do.

??? This is the essential behavior of Isearch, so you can search in
existing text.