Cycles: Add a soft min/max UI value for volume step size, usually a range from 0.01 to 1.0 is fine.
Cycles: Optimize math node without links to a single value node

Pretty straightforward implementation. Just needed to move some functions
around to make them available at shader compile time.
Fix T42389: Removed outdated comment from custom_nodes.py example script.

There was some confusion about the bl_icon attribute being optional. In
fact the functionality for hiding a tree type in the editor header is
now controlled by writing a poll function for the tree type instead,
which is more flexible and clean.

http://www.blender.org/documentation/blender_python_api_2_71_6/bpy.types.NodeTree.html#bpy.types.NodeTree.poll
Fix T42394: Copy Rigid Body Tools would not work as expected if dest ob had no rigidbody yet.

Adding new object to RigidBodyWorld obgroup is not a good way to do that, since it only
takes effect (create rigid_body for new objects) when you change current frame.

Better to use rigidbody.object_add() operator here!
Fix for Ctrl+Del/Backspace not setting text dirty
Cleanup: warnings, typos
Fix T42294: Bullet rigidbody point cache reading was using uninitialized
key values for velocity.
Correct stub
color tint