Heads-up: small change in autoconf support in ports

I finally got fed up of all the make bullshit in gnu-autotools, that
tends to fire up the wrong version of automake when it is present, and
prevents reliable builds of some ports.

(Old-timers know what pain this shit is)


So, there is now a code snippet in gnu.port.mk that touches the right
files in the right order, after running autoconf.

Specifically:
        .../Makefile.am
        configure.files
        configure.in
        configure.ac
        acinclude.m4
        aclocal.m4
        acconfig.h
        stamp-h.in
        config.h.in
        .../Makefile.in
        configure

I'm likely to add more files, as the need progresses (these are enough for
kde).

Some tribute to NetBSD is due: I didn't borrow any of their code, but I
remember reading such a snippet in their ports framework a while back...

Accordingly, those changes prevent autoheader to re-run automatically...
I've also added an autoheader keyword to CONFIGURE_STYLE, so that
autoheader gets rerun right after autoconf.

It's probably better to re-run autoheader more or less systematically,
except that... a few ports don't like this, so I am running a bulk pass,
and adding no-autoheader to the ports that have a problem with it, so
we'll probably end up with no-autoheader instead.

The improvements are quite worth the (very small) amount of odd behavior
I've seen so far, and that I am fixing.

-> if your ports tree behaves strangely, make sure you synched it all.
-> new ports and updates will need to take care of that.