Connecting indirect inputs for subnets

When expanding OBJ_SceneCacheTransforms, the child nodes will be connected to the subnet indirect input.
Auto-layout of expanded nodes
File parms channel reference their parent
SOP and Geo Path parms channel reference their parent
fixed crash in SOP info text
Adding interruptors for SceneCache nodes.

Expanding an OBJ_SceneCacheTransform and cooking a SOP_SceneCacheSource can now be interrupted using the escape key.
Merge pull request #80 from andrewkaufman/expandImprovements

Improvements for expanding SceneCaches in Houdini