Dupli Bugfixes!

It seems everytime I try to fix something here I break something
else, but anyway, another try at getting this to work properly.

Fixes for:
- Getting dupliverts/faces derivedmesh with orco caused wrong results
  on meshes in linked dupligroups with proxy, because modifier stack
  was revaluated with wrong object matrix, now gets orco another way.
- Fix render instances being hidden when original object was not added
  to the object render list.
- Changed the way object instances find their original objects, now
  works the other way around, original objects look for their instances
  instead.

There's probably issues still with recursive dupligroups..

source/blender/render/intern/include/render_types.h

@@ -174,7 +174,6 @@ struct Render
 
 	struct ObjectInstanceRen *objectinstance;
 	ListBase instancetable;
-	struct GHash *objecthash;
 	int totinstance;
 
 	struct Image *backbuf, *bakebuf;