Github #15: Relicense files marked GPL2 only to GPL2+.

Github #15: Relicense files marked GPL2 only to GPL2+.

I declare that now the contents of files util.c and ui_util.c are all GPL2+.

The majority of the code is from my own work (all functional util.c and some ui_util.c),
so I relicense it to GPL2+.
Contributions by Guilhem Bonnefille in util.c has been agreed to be relicensed to GPL2+.
Contributions by Matthew Hague in ui_util.c has been agreed to be relicensed to GPL2+.
Some code in ui_util.c has been reused from the Geany Project (https://www.geany.org),
 which has always been GPL2+ (thus previously incorrectly marked).

Signed-off-by: Rob Norris <rw_norris@hotmail.com>