Made render related methods non-const
Pass OSL's shading system to assemblies. Other small fixes.
Fixed error in last commit
Merge pull request #291 from est77/OSL_merge

OSL merge #3
removed unused code.
Merge branch 'master' of github.com:appleseedhq/appleseed
minor formatting fixes.
rendermanager.py 2.5: pings are now ordered from oldest to newest.
rendermanager.py 2.6: simpler, more robust display of pings.