Revert Automake license to GPLv2+. Automake will move to GPLv3+ once the Exception statement has been rewritten to use the new GPLv3 exception language. This change does not impact the COPYING file that may be installed by `automake --add-missing'. * COPYING: Revert to GPLv2. All uses changed. * NEWS: Update. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>