Blender Git Loki

* Added new paint API method paint_stroke_apply_subspacing, for various
things that need custom spacing (that is coaser than the brush radius),
and refactored the existing dyntopo spacing code to use it.

* Added option to topology rake to ignore brush falloff settings
(it forcibly uses Smooth falloff).

* Smooth and topology rake support custom spacing now.
+ This is especially important for the clay brush, which works
better at smaller spacings and with a bit of autosmoothing.
Now you can tell it to override the smooth spacing to be coarser,
leading to much better performance.

* Topology rake now has a projection setting similar to autosmooth
which defaults to 1.0 (to preserve current behavior).

The main motivation for this commit was to make topology rake work
better for normal brushes. This is now possible, however it tends to
make the brush slower and also the settings are a bit fiddly.
We might want to make dedicated brush presets for this.

Btw, the UI for brush settings are becoming a real mess. Help!