Added pixelAspectRatio to list of standard camera parameters.
Added pixel aspect ratio support to IECoreRI::Renderer.
Added pixel aspect ratio support to IECoreArnold::Renderer.
Bumped version to 9.0.0-a6 and updated Changes file
Merge pull request #335 from johnhaddon/pixelAspectRatio

Pixel aspect ratio
Take some files out of the line ending tweaks.