bug#10600: 24.0.92; `describe-char': text properties and [Show]

[Drew Adams]

> > When there are text properties on the char, `describe-char' 
> > (hence also `C-u C-x =') shows each of them using the button `[Show]'.
> 
> Please provide a precise step-by-step recipe to reproduce the problem,
> starting from emacs -Q.

I looked a bit closer.  The problem is apparently the same as for bug #10127:

The *Help* buffer being prepared has not yet been displayed, so it has no
associated window.  Yet the code calls (window-width) to determine the width of
the yet-to-be-displayed buffer.  This is obviously wrong.

The current window for that calculation does not correspond to *Help* at all.
It is wrong to assume that *Help* will be displayed in a window having the same
width as the window where the help command is invoked.  In particular, when
pop-up frames are used or *Help* is a special-display buffer then its width will
not, in general correspond to the initial window.  Another case is where windows
are split side-by-side.

It's simply misguided to base the assumed *Help* window width on the width of
any existing window.  It makes more sense to do something like this:

Use the maximum default width for *Help* _buffer text_, which is no doubt
something like 70 (less than 80, in any case).  We already go to the trouble of
wrapping help text at such a limit.  That limit should be also the basis for
determining the width of this help display.