removed redundant comments.
cosmetics.
fixed build by removing unused variables.
added missing #include statements when OSL is enabled.
fixed OSL build on Windows by adding explicit namespace qualifiers.
fixed warnings due to lossy implicit conversions.
some external code defines 'far' as a preprocessor symbol; make our code immune to this.
updated copyright notices.
updated copyright notices, plus minor cleanups.
use pimpl idiom renderer::ShaderGroup class because it is DLL-exported.
fixed warnings due to lossy implicit conversions.