To answer my own question, the extreme tolerance in the planarity test for
polygons does not seem to be necessary.  I recompiled POV-Ray, changing the
line

    if (fabs(d) > ZERO_TOLERANCE)

in Compute_Polygon (Polygon.c)

to

    if (fabs(d) > 0.0002)

This is the tolerance value I used to set up the polygons in the first
place.  Now POV-Ray will do my files with no problems - I attach a sample.

Assuming that this causes no other problems, this would obviously be a
useful change in POV-Ray.  To have to convert a set of corners to triangles
or rotate back and forth seems to be unecessary extra work.  Again the
tolerance value could be an option, if there is any reason for having a
tolerance of 0.0000000001 at all.

Eric

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