Fix build on OS X using all external libraries (except xerces)
Add installation command for easier packaging in future
Fix building on Linux using all external libraries (except xerces)
Added more directory to be installed so that the package is more complete.
a sun light can now retrieve the sun position and the turbidity from an environment EDF.
Merge branch 'master' of https://github.com/nyue/appleseed into nyue-master

Conflicts:
	src/appleseed.python/CMakeLists.txt