Combined patch with the following changes:
- Don't add wxGLAttributes::Defaults() when the attributes-list is NULL.
- Add display default attributes used in wx versions before 3.1 when the
attributes-list is NULL. These attributes are different for each platform.
- Fix wxMSW PixelFormatDescriptor initialization.
- Don't set color buffers when RGBA() is used.
- Fix setting colour sizes in OS X and a few other fixes.
- Make documentation more clear about these subjects.
Closes#17425.