Blender Git Loki

Bug fix: Render and 3d view conflict over ob->imat

* For rendering every object's inverse matrix "ob->imat" needs to
be in render view coordinates, but for drawing in 3d view it needs
to be in global coordinates. Originally (way back in historical
times) ob->imat was only used for rendering, but over the years
other uses came up too. Before 2.5 this wasn't a problem as
rendering was a totally blocking operation, but with the new
"interactive ui while rendering" the problems started. Basically
any update that redrew the 3d view while rendering (like rotating
the scene with mouse) updated the inverse matrix into global
coordinates thus invalidating it for the render, leading to all
kinds of strange discontinuities with textures and volumetrics.

* Problems were very easy to achieve using orco/object coordinates
for pretty much any textures (bump, point density, volume, sky),
for examples see bug reports 24906 and 25229. Render baking normals
in object coordinates was wrong most of the time too.

* Now there is a separate inverse matrix ob->imat_ren that's
calculated at the beginning of rendering and is used in all places
inside render code where it's needed. This way the original ob->imat
can change at will during rendering without causing problems.