autoconf.texi has hard-to-maintain @node lines

[Paul Eggert]

Here's a little problem that I ran into when composing the earlier doc
patches.  Is there any reason that autoconf.texi has lines like this:

  @node Shell Script Compiler, Autoconf Language, Writing configure.ac, Writing 
configure.ac

when it could just have lines like this instead?

  @node Shell Script Compiler

The latter, more modern style is easier to maintain (it would have
made my patches smaller, for example), and is used in the other .texi
files like install.texi.  Is there any reason we shouldn't change
autoconf.texi to use the more modern style?  I can volunteer to do
this little task.