Blender Git Loki

* Fix for volumetric rendering. It previously wasn't multiplying
the emission component by the density at the current point, which
made the volume too bright in less dense areas. This made it look
too rough, as opposed to smooth as it should be. This makes the
particle rendering look *much* better, thanks a bunch to ZanQdo for
complaining and kicking my butt to make me realise the error.

Here's an example of how smooth it looks now:
http://mke3.net/blender/devel/rendering/volumetrics/smoke_test03.mov
http://mke3.net/blender/devel/rendering/volumetrics/smoke_test03.blend

Settings in existing files will have to be tweaked a bit, since
what they were set up for before, was incorrect.

* Added two new interpolation types to Point Density: Constant and
Root. These work similarly to in proportional edit for example,
just gives a bit more choice over how hard-edged the particles
should look.