Thomas Hellstrom authored Aug 07, 2017 and Brian Paul committed Aug 17, 2017

Fix the following problems with this test:

1) The spec is not referring to glXChooseVisual attributes, only to
glXChooseFBConfig attributes. So use glXChooseFBConfig.

2) Make sure we have an alpha channel.

3) Call piglit_dispatch_default_init before issuing GL commands.

v2:
- Test also alpha.
- Test also frontbuffer.
v3:
- Addressed review comments by Brian Paul.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>