Blender Git Loki

Depsgraph optimization: Don't schedule tasks for empty "NOOP" nodes.

Currently a lot of the nodes in the new dependency graph are empty placeholders
for organizational purposes. These nodes would, however, still be assigned a task
which gets scheduled and takes up some time for worker threads to pop from the
queue and run. This can be avoided by skipping these nodes during depsgraph
scheduling, and scheduling their childrent right away. Gives a few percent speedup
in BlenRig.