[Gtkradiant] libpng15 support

[Rudolf Polzer]

On Sun, Mar 11, 2012 at 07:25:22PM -0700, Nerius Landys wrote:
> I am away this week so I can't test this patch right now.
> My plan would be to just test the patch to make sure it does not break
> stuff on Debian 6.0.  If that is the case I would probably go ahead
> and commit it.
> 
> I'll do it Saturday if nobody (TTimo hint hint) gets around to it first.

The minimum requirement for the patch is libpng14. libpng12 does not have
png_jmpbuf().

Best regards,

Rudolf Polzer