Blender Git Loki

Generalized algorithm for constructing node blocks based on local arguments.

Nodes can have expression inputs and override argument nodes with local
variables. This means that a local block must be created for each expression
input. The boundaries of such blocks are defined implicitly by upstream nodes
which define their own local arguments (or ultimately by the graph arguments).

The current version is still not quite generic enough to allow arbitrary
nesting of blocks, but it should ensure that expressions don't include all
the parent nodes which don't depend on local arguments and therefore should
be calculated in the parent block (a form of constant folding).