[rekonq] Enable the raster graphic system by default on X11

[benjamin.poulain at nokia.com]

> The opengl graphicssystem is seriously kicking ass (performance-wise) :-D
> With it I get values from 46–60 FPS (60 is the refresh rate of my monitor, so that’s the max. FPS it can show).
> 
> The opengl graphicssystem shows some weird side effects though, like the fonts not being anti-aliased etc, which are problem the raster graphics system does not have.

Unfortunately, as you noticed, the graphics system opengl is yet not good enough for Webkit. For example, it is not reliable for stupidly big images.