updated manifest for standalone appleseed.foundation library (version 1.7).
updated plugs for standalone appleseed.foundation library.
added test for foundation::Logger in standalone appleseed.foundation library test program.

fixed manifest and plugs to make the test pass.
fixed build error on OS X by removing unused functionality.
Merge remote-tracking branch 'upstream/master' into OSL_specular_bsdfs
Added more comments.
Added reference image for simple glass scene.