bug#10542: 24.0.92; `Search' field in Customize

[Drew Adams]

> > This search field is unlike any search field a user has seen before
> > (at least this user): whitespace, particularly whitespace 
> > at the field beginning and end, is significant (searched for).
> 
> Please provide a precise step-by-step recipe for reproducing 
> the problem you have in mind, starting from emacs -Q.

I did that:

> click the mouse somewhere in the middle or at the end of
> the search field, type a word/symbol, and click `Search',
> only to see "No matches".

Since that and the other descriptions I gave of the problem are apparently not
enough, let me try again.

1. emacs -Q

2. M-x customize-option <ANY OPTION YOU LIKE>

3. Click mouse-1 somewhere past the beginning of the Search field.

4. Type `link' or some other substring of an option name.

Resulting message:
"No customizable items matching    link"

This is clearly unusual and unexpected behavior - and unexplained.

As I said, this is clearly a feature - good, not bad.  But it needs to be made
clear to the user.  I proposed some ways in which that could be done.

Most users are not used to whitespace, particularly leading and trailing
whitespace, being significant in a search field, without the use of delimiters
such as quotes.

Additionally, any no-hit message should clearly delimit the search string: wrap
it in `...' or highlight it or something, to set it off from the message text
that refers to it.  The search string is, in fact, being quoted without any
quote indication.