[2.1.0] Bump freetype minimum version to 2.2.0?

Hi,

While working on a bug (http://bugs.libgd.org/?do=details&task_id=42),
I came across one of my todo for gd-2.1.0. I like to set the minimum
Freetype version to 2.2.0 instead of 2.x.

Freetype stable branche is 2.3.0 now, 2.2.x is a couple of years old
and contains many critical fixes. It wil help a lot to clean up our
encoding support as well as improve the rendering quality.

Is there any objection?

Regards,
--Pierre