Subject: Artifacts in spec1.ppm

(This message is being sent to all CPSC 215 students and TA's)

If you encounter oddball reflections on the outsides
of your spec1 spheres you may be afflicted by FAILURE
TO TEST for negative "t" value in you sphere_hits functions.

Negative "t" can't happen for rays fired from the viewpoint
but CAN AND WILL happen for reflected rays.

Basically ALL hits functions should test for negative t
and return -1 whenever t is negative.

Also remember not to allow infinite plane hits with positive
z coordinates