graphics/{,py-}openshadinglanguage: sort out Makefile, pet portclippy, add graphics/partio as dependency

Grab silently graphics/partio (small library for reading, writing, and
manipulating a variety of standard particle formats GEO, BGEO, PTC, PDB, PDA)
if installed.
It's possible to create build option PARTIO and prevent search partio with
PARTIO_CMAKE_OFF=-DCMAKE_DISABLE_FIND_PACKAGE_partio:BOOL=ON, but partio is
small and is on by default by ustream - so add it as mandatory dependency.

Also rename renamed by upstream ENABLERTTI to ENABLE_RTTI and pet portclippy.

PR: 279457
Approved by: Shane <FreeBSD@ShaneWare.Biz> (maintaner)