Merge pull request #592 from est77/master

Added missing break statement.
Merge pull request #593 from est77/master

Added some missing things to the api headers
Merge pull request #594 from est77/master

Fixes for plugin displays
fixed ray-curve intersection, and heavily refactored the curve reordering code.
Merge branch 'master' of github.com:appleseedhq/appleseed
tweaked appleseed.package sample configuration file.
appleseed.package.py 2.3.12: fail with a clear error message if a configuration value is missing.
cosmetics.
minor code tweaks.
cosmetics.
small code factorization.
fixed bug: slider can no longer be moved after entering 0 in text box.
Added missing material models to the API.