Support hclassic and bhclassic
Fixes bug where empty particle set will crash on findNPoints() and also add ptf support

Fixes Bug #25741
Fixes Bug #25742

Conflicts:
	src/lib/core/KdTree.h
	src/lib/io/ParticleIO.cpp
Updated scons scripts to put tests in tests/partio directory.

Signed-off-by: Mark McLaughlin <mark.mclaughlin@disneyanimation.com>

Conflicts:
	Makefile
	src/doc/SConscript
	src/tests/SConscript
build: tests go in share/test/partio