Some little changes and bugfixes.

 - RenderTexture unbinds itself on frame buffer configuration fail,
   before raising an error.
 - RenderTexture was potentially doing integer division on texture
   size ratio calculation
 - GL21 LineVector software draw could possibly be called before
   line vertices had been created.
 - Line/RGB vector command line args were not enabled
 - RGBVector was not initialising texture interpolation correctly