Texinfos handling

[Akim Demaille]

I'm contemplating LaTeX support, so I glanced at the Texinfo code,
and started some clean up (white space, will be a separate checkin if
accepted: covers only the 4 Texinfo related functions).  I stumble
on a simple question: what is the correct style for function calls?
I see there are still many &define_variable, where I would write
define_variable (cleaner, enables proto checking, but less Emacs
friendly, and therefore slightly less colorful).  Is there a guide
line?