How can I disable auto compositing? I am working in the compositor with a lot of textures and distort nodes, which makes it very slow (easily 20-30 seconds to composite.) Every time I make a change, it re-composites. This is fine when just moving nodes around, but there are other operations that you can't do until it finishes. For example, Undo. If I want to undo 3 or 4 times, I have to wait for it to finish compositing every time. Likewise if I want to work in the texture nodes part of the nodeviewer, I am often waiting on the compositor to get node previews.

Is there a way to tell it not to automatically composite? I want to make a bunch of changes and be able to see the part I'm working on in a viewer node, but not run the entire stack. I understand that I can mute all the other nodes I'm not using, but that is troublesome and doesn't help with the Undo issue or problems when working in texture nodes. I can be stuck waiting on the compositor even when doing Undos on meshes or materials, which are entirely unrelated.
I find that pressing the "use nodes" works for this task (next to backdrop tickbox). When you want Blender to composite again just re-enable it.

screenshot: