Fixes crash when merging CortexPrimitives in Houdini 13.

Added merge constructor and fixed signature of stashed() for H13
Merge pull request #242 from andrewkaufman/mergeConstructor

Fixes crash when merging CortexPrimitives in Houdini 13.
Fixed a bug where the EXRImageReader would interpret Deep EXRs as valid.
Merge pull request #244 from goddardl/EXRImageReaderBug

Fixed a bug where the EXRImageReader would interpret Deep EXRs as valid.
Fixed linking of IECoreNuke for Nuke 8.

The libDDImage in Nuke 8 links against libRIPFramework, so that library must be available at build time in order for the configure tests to pass. The -L flag isn't used when searching for the dependencies of a library, so we use the -rpath-link flag to specify where libRIPFramework is to be found.

Unlike the -rpath flag, -rpath-link only has effect at compile time, and doesn't affect linking at runtime.
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.
Merge pull request #252 from johnhaddon/nuke8

Fixed linking of IECoreNuke for Nuke 8.
Implemented some transformation matrix features

Including coordinateSystem()
SXRenderer now only has a world transform
Merge pull request #248 from davidsminor/sxRendererFixes2

Sx renderer fixes2
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
Added missing ifdef
Updating minor version and Changes file
Fixed a bug with IECoreNuke::SceneCacheReader that was causing hanging and crashing.
Merge pull request #254 from goddardl/SceneCacheBug

Fixed a bug with IECoreNuke::SceneCacheReader.
Updating changes
Fixed failing test case