With GNU make, using .PHONY leads to the same result as using
the "FORCE" hack, but unlike FORCE is not a hack. Since we do not
plan to use any other make implementation than GNU make, let's not
provide FORCE in nmk.

For more details about why PHONY is better than FORCE, see
http://www.gnu.org/software/make/manual/make.html#index-FORCESigned-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>