Blender Git Loki

Adapted the node blockify procedure to the new concept of expressions and variables.

The internal bvm nodes now can contain (implicit) cyclic connections, owing to the
connection of variable inputs to local variable outputs of kernel nodes. These link
cycles are never created explicitly by the node parser (pynodes), but are a result
of the semi-functional programming nature of the nodes: each node constitutes a
function of the local variables defined inside a kernel block. When the nodes are first
constructed from the user-level nodes these inputs are left unbound, and are then
resolved backwards as the individual node functions are inlined.