perfbook.tex: Modify definition of \nbco{}

It turns out that \nbco{} can't hold "#" character.
Modify its definition to use the combination of a \co{} variant
and \hbox{}.
Also add a macro named \qco{} which has quotation marks around
\nbco{}.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
1 file changed