Changes in version 3.1:
The scene description language in POV-Ray 3.1 is not entirely
backwards-compatible with earlier versions of the POV-Ray scene
description language. The 'halo' feature in earlier versions
is obsolete and has been entirely replaced with a 'media' feature
which works better. Because older files making use of 'halo'
will not render in POV-Ray 3.1 without substantial modification,
you may wish to rename executables for pre-3.1 versions of POV-Ray
if you would like to be able to render such older files. It should
be noted that .povrayrc as described below can only refer to one
version.
