Added IECore::EXRDeepImageReader and test cases.
Modified the SConstruct so that the EXRDeepImageReader is only built with OpenEXR versions that support deep images.
Changed the EXRImageReader to fail when trying to load a deep exr.
Added IECore::EXRDeepImageWriter and it's bindings and test cases.
Moved the EXRDeepImageWriter compression options into their own scoped binding.
Removed a duplicate test case.
Merge pull request #253 from goddardl/EXR2

EXR2 Deep Image Reader and Writer