bug#16802: @w for long option names

[Karl Berry]

In a couple places, coreutils.texi uses @w around (bare) long option
names.  These are the ones I noticed:

621:@item @address@hidden
1268:The @address@hidden (@option{-t}) option allows the @command{cp},
1312:operating on it.  The @address@hidden option enables

I'm guess the point is to avoid line breaks at the internal hyphens
(there would/should never be line breaks at leading hyphens).  In which
case, a cleaner/more general approach would be

@allowcodebreaks false

Then there is no need for sprinkling @w throughout the source.
We added that in Texinfo 4.11, released 2007.

(It belatedly occurs to me that we should make @option, specifically,
always disallow line breaks at hyphens.)

karl