Any idea how to make it so we only need one of these `process_events` call (or maybe none) to get a usable context?

BTW, we should just add a context manager to `vispy.app` for testing since these lines are starting to be used a lot. Something like:

```
with app_opengl_context():
    opengl_things()
```
would be excellent. Basically it would be the five lines above this, plus the `c.close()` moved into a context manager. WDYT?