Fixed bug #4837: "Knobs not found" warning messages.
The bug only appears when loading the LensDistort node UI for the first time with a file sequence specified. The cause was the early termination of the knob_changed() method before an update
to the dynamic knobs was made. The fix also the code simpler to read.
Fixed an issue where the artefacts were appearing around the edges of the bounding box despite the "black_outside" flag being turned on.
An additional result of this fix is that the distorted image is no longer clipped slightly around the edges.
Fixed SceneCache build problem on OS X.
Removed IECoreGL/Lights.h.

It was unecessary before, isn't used anywhere, and refers to deprecated OpenGL functionality we wish to move away from.
Removed IECoreGL/GLUT.h.

We don't have a dependency on GLUT any more, and we should have removed the header when we removed the dependency. Also fixed inaccurate comment in IECoreGL.h.
Merge pull request #147 from johnhaddon/removeGLUTHeader

Removed IECoreGL/GLUT.h.
Merge pull request #146 from johnhaddon/removeGLLights

Removed IECoreGL/Lights.h.
Merge pull request #145 from johnhaddon/sceneCacheMacBuildFix

Fixed SceneCache build problem on OS X.
Merge pull request #143 from goddardl/LensDistortMissingKnobError

Fixed bug #4837: "Knobs not found" warning messages.