Real full-screen mode

[Tux]

While testing other rendering modes, I discovered that the "drawpixels" mode for rendering in opengl was broken, it produced a black screen if "opengl overlay interface" was enabled, and it is enabled by default. It took me more than 1 hour to find out, a very stupid thing, but which seems to be here since 2013 !!!

Ok, DrawPixels is not really interesting, I just keep it in case someone with a very broken opengl setup tries to use it because it can't use the default render to texture, but broken for almost 10 years... !!!!

Anyway it was just because the overlay text interface was temporary disabling GL_TEXTURE_2D before rendering its text which is ok, but then it enabled it again, which is good for the default texture rendering, but which breaks very efficiently the drawpixels renderer !

Anyway... !