Blender Git Loki

Sculpt: Multires

* Displacement coordinates are now stored differently, as a grid per
face corner. This means there is duplication of coordinates, especially
at low subdivision levels, but the simpler implementation justifies it
I think.
* ToDo: conversion of existing multires files (2.4x or 2.5x), loading them
may even crash now.
* Editmode preservation/interpolation code also has not been updated yet.

* Multires now works on the CCGDerivedMesh grids instead of CDDerivedMesh,
which should be more memory efficient.
* There are still bad memory peaks (if you're using 32bit) when subdividing
or propagating displacements. Though at least there should be no huge
memory blocks allocated, which windows is now to have trouble with.
* Still found some weird spike artifacts at lower multires levels, some also
happening before this commit. Perhaps computation of tangents needs to be
tweaked more.

* Multires modifier now has viewport, sculpt and render levels. Also the
levels have been made consistent with subsurf, previously the same level
of subdivision was one less for multires.
* Both multires and subsurf modifier now can have their subdivision level
set to 0 for no subdivision.