Blender Git Loki

PSculpt: Pressure and Influence Cleanups

* Use tablet pressure to control strength of effect. More work is still needed
to be able to turn this on and off as needed (i.e. the little toggle for pressure
sensitivity)

* Currently, all places which use this now use linear falloff. This again should
be controllable by the user.

* TODO: Discovered a bug with how the "data" structs are getting used. It turns out
that the pso->data is not getting used, while a separate "clean slate" is getting
created each time.