bug#6755: 24.0.50; Customize buffer is too wide. Put doc string on separate line.

[Drew Adams]

> Starting with a newline didn't look very nice.  Most of the option
> values are short, and moving them away from the button made the
> interface less understandable.
> 
> I think the right solution is to output the string where it 
> is now, but to fill it if it's too long.

Why not just start it on a new line if it would wrap?

IOW, instead of just filling, if it would wrap then start it on a new line.

(You could also then fill it, after starting on a new line, but I doubt that
:tag string will be more than 70 chars.  Still, it wouldn't hurt to do that.)