GRIM: Use GLfloat instead of float when passed to gl* functions.
GRIM: Disable GL_LIGHT0's default specular component.
GRIM: Replace intensity divisor with attenuation.
GRIM: Always set light's GL_SPECULAR.
GRIM: Use specular lighting.

A few sets where spot lights are present: hq (elevator, projector),
do (window), al (light above garage door).
GRIM: Set a spot exponent to simulate DirectX's penumbra.

Effect is especially visible near set do's window.
Merge pull request #893 from vpelletier/fix_lights

Improve light intensity