Blender Git Loki

Orange: more float buffer support;

- Image textures use float colors now, when present. Works for mipmap too,
and for AO skycolor (probes)
- Backbuffer option uses float buffers too. Note that rendering OSA will
resample the backbuffer, filtering it... will need to be solved with the
new composit stage
- LMB sampling in image window now shows float color too

+ bugfix in imbuf, filtering for float buffers had an error.