CL_GraphicContext::get_pixeldata patch for GL/GL1 target

[huntercool]

Here's a patch to get screenshots working.

Tested on ATI 5870, Windows 7.

Have not tested Nvidia cards.

[rombust]

Maybe that patch will also require a "framebuffer active" check for the GL target, like you did for the GL1 target.

So, you can still get pixels from the framebuffer (without calling clReadBuffer(CL_BACK);)

I think there is a "framebuffer_bound" bool in GL that you can use.

[huntercool]

There sure was a "framebuffer_bound" in the GL target.

This patch should work.

[rombust]

Patch applied to ClanLib 2.2 and 2.3 svn

Many Thanks