Blender Git Loki

Transitive reduction optimization for operation relations.

This removed redundant relations between operations, implementing the
transitive reduction algorithm:
http://en.wikipedia.org/wiki/Transitive_reduction

The current implementation is a bit naive, but can be improved later.

Using this optimization gives more flexibility in the build procedure,
since we don't need to have fully defined relations in a component
before adding external relations.

Performance would only be improved in some extreme cases probably
(huge amount of redundant relations), it should be much more dependent
on a good scheduling heuristic.