added global ID to parallel_for_for
added global ID to parallel_for_for_prefix_sum
added parallel_reduce
added reduction to parallel_for_for_prefix_sum
cleanups in parallel_for
added missing files
cleanups in parallel_for_for
cleanups in parallel_for_for
cleanups in parallel_for_for
cleanups in parallel_for_for
Merge branch 'devel' of https://github.com/embree/embree into devel