Png support

[qudos]

Hi,

I'd already noticied some time ago what since png looks like was
supported in q2max,  not was really, i.e, barrels and jacket armor
from pak13?.pak are in png format but q2max is not able to load it.

Well, i've attached a patch for png support, this patch is valid only
for q2max and tested only in glx driver.

Basicly requires little changes, these are, Makefile,
ref_candygl/gl_image.c and ref_candygl/gl_rmisc.c and also the new
added gl_png.c file.

The diffs were done against q2-0.16.2

Just try it, put some conback.png file in your baseq2/pics.

http://qudos.quakedev.com/tmp/patch_q2icculus0.16.2_png.gz

Cheers