Fix #34863: bge.render.makeScreenshot from Blender was only saving PNG files,

while the docs said it followed the settings in the Output panel, other file
formats work now.

Benderplayer still only saves PNG now as documented, but I cleaned up the code
there to reuse existing imbuf functions rather than using own libpng code.

doc/python_api/rst/bge.render.rst

@@ -97,7 +97,7 @@ Functions
    The standalone player saves .png files. It does not support color space conversion 
    or gamma correction.
    
-   When run from Blender, makeScreenshot supports Iris, IrisZ, TGA, Raw TGA, PNG, HamX, and Jpeg.
+   When run from Blender, makeScreenshot supports all Blender image file formats like PNG, TGA, Jpeg and OpenEXR.
    Gamma, Colorspace conversion and Jpeg compression are taken from the Render settings panels.
    
    :type filename: string