Autotools update.   Read ports/UPDATING 20100915 for details.

Approved by:    portmgr (for Mk/bsd.port.mk part)
Tested by:      Multiple -exp runs

Reassign the autotools-related ports to a new mailing list,
autotools@FreeBSD.org.  This is for individuals willing to put in
the hard work to generate patches and work with portmgr as we put
them through -exp runs and work through port breakage that they
create.  (A huge number of ports depend on these, so -exp runs are
required.)

Thanks to aDe@ for all the thankless work he's done over the years
to tame these beasts.

Hat:            portmgr

Update CONFIGURE_ARGS for how we pass CONFIGURE_TARGET to configure script.
Specifically, newer autoconf (> 2.13) has different semantic of the
configure target. In short, one should use --build=CONFIGURE_TARGET
instead of CONFIGURE_TARGET directly. Otherwise, you will get a warning
and the old semantic may be removed in later autoconf releases.

To workaround this issue, many ports hack the CONFIGURE_TARGET variable
so that it contains the ``--build='' prefix.

To solve this issue, under the fact that some ports still have
configure script generated by the old autoconf, we use runtime detection
in the do-configure target so that the proper argument can be used.

Changes to Mk/*:
 - Add runtime detection magic in bsd.port.mk

Handle an edge-case where lang/gawk is installed prior to any autoconf*
ports, which then results in an implicit dependency on gawk, with the
obvious bad things happening should gawk be later removed.

Note that because this is an edge case, which most folks will not run
into, and because it doesn't change the default package, I am not
bumping PORTREVISION as suggested in the original patch.

PR:     125101
Who:    matthias <dot> andree <at> gmx <dot> de

Missed patch.  Sigh.

Fix missed comment update

Introduce autoconf 2.62, which can now be used by other ports with the
appropriate USE_AUTOTOOLS stanza.

Note that the mass-conversion from autoconf 2.61 -> 2.62 will take place
at a later date.