Changes to rendering logic, incl water surface flicker fix, plus other fixes.

This commit changes a bunch of internal rendering logic to
use FBOs in a way that doesn't violate the GL spec.
The water surface FBO's output texture was bound for reading
while at the same time rendering the water surface back into the
same FBO! Depending on the card/driver/load/zoom factor/moon phase,
this could lead to water surface flickering, chessboard effects,
and other visual glitches.
In order to fix this an extra FBO is needed.
In theory this is a simple fix but in practice this is the Aquaria
codebase and everything is more complicated than it has any right to be.

Couple other things:

- FBOs no longer have a depth renderbuffer. Aquaria never uses the depth
buffer for anything, so this can go to save some memory.
Also remove renderbuffer GL function pointers.

- Make FBOs multi-"paged". This is supposedly more efficient on desktop GL,
if glDrawBuffer() supports GL_COLOR_ATTACHMENTn. This is currently checked
via the presence of glDrawBuffersARB().

- Main core FBO now has 2 pages becaus it's needed for the water surface.
The same 2 pages are later used by the after effect manager to ping-pong
postprocessing shaders. Remove private after effect FBO.

TODO:
- There's still a bug in the one-fbo-multiple-binding-points code path.
-> for now glDrawBuffersARB must be NULL to work properly.

BBGE/ScreenTransition.cpp

@@ -81,11 +81,12 @@ void ScreenTransition::reloadDevice()
 void ScreenTransition::capture()
 {
 	assert(screen_texture);
-	core->render();
+	core->renderExternal();
 
 	if (screen_texture)
 	{
 		glBindTexture(GL_TEXTURE_2D,screen_texture);
+		glReadBuffer(GL_BACK);
 		glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, windowWidth, windowHeight);
 		glBindTexture(GL_TEXTURE_2D, 0);
 	}