The helper function `make_freestyle_edge_mark_hash()` was referring to the
original mesh to determine Freestyle edge marks for individual derived mesh edges.
This is no longer necessary now that derived meshes deliver CD_FREESTYLE_EDGE
and CD_FREESTYLE_FACE layers of their own. The reference of the original mesh
was also inappropriate since the edges coming from one of the operands of a boolean
modifier don't have proper CD_ORIGINDEX values but ORIGINDEX_NONE's.
Many thanks to Sergey Sharybin for patch contributions and discussions.
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