Improve light intensity

Reduces a log the difference with original's software renderer. The following sets were checked: mo, ga, al, do, su.
In do and su, there is a light which seems misbehaving (chepito_light in su, newlight1 in "do"): they are removing light from the scene in some conditions. Tests were done with these lights disabled when this happens. More details:
In su, chepito's light darkens scene center when intensity is low (=when chepito is far).
In do, the window spotlight darkens hall-side of the room and the bottle.

There are still glitches around "do"'s window: if you stick to the left (screen-wise when camera points away from the window) wall and walk toward the window, polygons get illuminated a bit crudely. Setting GL_SPOT_EXPONENT improves this, but reduces peak light intensity somehow, so I did not include a change for this.