Merge: gamnit: fix field of view issues

Erroneous code at creation of the perspective matrix caused a wider than requested frustum and field of view. This caused issues in other gamnit code:

* The service `camera_to_world` had to multiply the result by 1.72 to correct the deformation.
* In `asteronits`, the world was not filling the screen, only part of it.
* In general, it created a cool but not desired wide angle lens / fisheye effect.

After the fix, some clients might have to widen the requested visible area, usually set with `reset_height`. We may have to lower the default `field_of_view_y` as it is a bit high.

Pull-Request: #2307
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Jean Privat <jean@pryen.org>