Blender Git Loki

Bugfix #5030

- Removed obsolete IRIZ image support from menus.
This was a Blender-only version of SGI Iris images, used internally in
the nineties because it was the only format supporting Z easily
A much better Z exporting - and industry compliant - is via OpenEXR

- Scene strips in Sequencer now get Z buffers as well. This is only in
float format, containing actual distances from the camera.