Upgrade contributed gperf, m4 and flex

Hi,

I plan to upgrade gperf to the latest GPLv2 version: 3.0.3.
I also plan to upgrade m4 syncing code from openbsd, taking code from netbsd
(improve gnu m4 compatibility).
and last: upgrade flex to the latest upstream version (it will need the m4
upgrade) while here I'll move back flex to contrib/

patches can be found there: 
http://people.freebsd.org/~bapt/flex-update.diff
http://people.freebsd.org/~bapt/update_m4_from_openbsd_and_netbsd.diff
http://people.freebsd.org/~bapt/upgrade-gperf-to-3.0.3.diff

While pushing this upgrade I plan to bump the FreeBSD_version so that ports can
easily benefit of this upgrades,

regards,
Bapt