creating gsoc branch for Nicholas Bishop
== Multires ==

Added a Multires modifier, including a simple interface. (The modifier and interface are entirely nonfunctioning.)
== Multires ==

Hid the old Multires panel.
== Multires ==

* Added an MDisps customdata layer to store multires displacements in
Merged with trunk (15144)
Big commit with initial support for sculpting of meshes with the multires modifier.

With this commit, the displacement custom data is being applied to a subdivided version of the base mesh using a modification of CCGSubsurf.

Sculpting on the highest level of the multires mesh now works, with (at least) these caveats:
* Only the plain 'Draw' brush works for now
* Normals aren't being updated during sculpting, so it doesn't actually look right yet
* When displacements are applied or calculated, only interior face points are handled, so original vertices and edge vertices will look wrong after switching levels.
Enabled updates of normals when sculpting on a multires mesh (only works for smooth meshes now)
Fixed updating of normals during sculpting for non-smooth multires meshes.
Fixed updating displacements for meshes with more than one polygon
Displacements over subdivided edges work correctly now (both for display and updating the highest level.)
Vertices in the base mesh now get displaced.
Fixed the other sculpt brushes so they work on multires meshes.
Fixed "exploding" vertices in the base mesh.
Fixed saving/loading of MDisps. This took longer than it should have because of a bug in SDNA, noted in the MDisps struct.

Undo/Redo should work correctly as well.
Fixed going into editmode with unsaved disps.
Re-grouped the three sculpt panels.
Merge with trunk (r15316)
Force an update of mesh disps before subdividing
Added displacement subdivision; displacements aren't lost when multires-subdividing now. Subdivision is not yet entirely correct; edges and corners aren't handled correctly, so there is still a visible seam.
Finally, subdivision with multires modifier works fully.