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Initial implememtation for dupli objects

Now dupli groups, objects, particles, ... are all working.

This introduces a flag for the iterator to determine whether we go over
Set and dupli objects or not.

Important to remember to keep the iteration of DEG_ as readonly.

Cycles is not working well for dupli groups, and it's memleaking
for dupli particles. So for now we iterate over main objects and set
only, not dupli.

To change that go in rna_scene.c and:

-DEG_OBJECT_ITER(graph, ob, DEG_OBJECT_ITER_FLAG_SET)
+DEG_OBJECT_ITER(graph, ob, DEG_OBJECT_ITER_FLAG_ALL)

Review and suggestions by Sergey Sharybin