Stop dyntopo updates from happening in masked areas

Fixes [#34348] Collapse short edges affects masked geometry
/projects.blender.org/tracker/?func=detail&aid=34348&group_id=9&atid=498

Fixed by disallowing topology updates on edges with a vertex masked at
50% or greater. This is a necessarily arbitrary choice; can't do
halfway updates for topology like we can with displacement.

Fix sculpt view normal for transformed objects

Patch from Antony Riakiotakis, thanks!

Fixes [#34641] "Front Faces Only" option in SculptMode behaves weird
projects.blender.org/tracker/?func=detail&aid=34641&group_id=9&atid=498

Fix for collapse-edges crash in dyntopo

Was incorrectly testing for a vertex in a set with BLI_ghash_lookup
rather than BLI_ghash_haskey; the key in this case is always null so
the test failed.

This could leave the PBVH in an inconsistent state, since the
top-level map of BMesh vertices to PBVH nodes would indicate the
vertex was in a node, but that node wouldn't actually have any faces
using the vertex. That inconsistent state would eventually lead to a
crash in pbvh_bmesh_vert_remove().

Fixes
http://projects.blender.org/tracker/?func=detail&atid=498&aid=34370&group_id=9

Fix for harmless uninitialized-variable warning

Fix performance regression with anchor brush in sculpt mode

When restoring coordinates in sculpt mode (used for several brushes
including anchor brush), can use sculpt_undo_get_node() for
non-dyntopo sculpting instead of sculpt_undo_push_node().

This should bring speed of anchor brush back to 2.65 level for regular
mesh/multires sculpting.

Fixes projects.blender.org/tracker/?func=detail&atid=498&aid=34208&group_id=9

Ensure that mask layer exists in sculpt mode after multires subdivide

Sculpt mode requires mask customdata layer for multires and ensures it
exists on entering sculpt mode. However, sculpt mode only considers
multires to be active if the level of subdivision is not zero, so it
does not add mask for unsubdivided multires meshes. If the multires
mesh is subdivided while in sculpt mode, no mask was present leading
to weird drawing and crash on use of the mask brush.

Fixed by doing the same thing in multires_subdivide_exec() that is
done in ED_object_modifier_add(), which is to check if sculpt mode is
active and add mask layer if so.

Fixes [#34190] Viewport artifacts when using Multiresolution modifier
projects.blender.org/tracker/index.php?func=detail&aid=34190&group_id=9&atid=498

Remove loose edges created during undo in dynamic-topology sculpt mode

Fixes [#34043] "Dyntopo: noise appear during sculpting (parasite edges)"
projects.blender.org/tracker/index.php?func=detail&aid=34043&group_id=9&atid=498

Check for deletion before moving vert in dyntopo collapse edge

Fixes [#33964] Dyntopo crash with edge collapse + undo
projects.blender.org/tracker/?func=detail&aid=33964&group_id=9&atid=498

Remove dynamic-topology flag from mesh when entering sculpt mode

This will be enabled if the file was saved with dynamic topology on,
but we don't automatically re-enter dynamic-topology mode when loading
a file so remove the flag.

Fixes bug [#33956]
projects.blender.org/tracker/?func=detail&aid=33956&group_id=9&atid=498

Add missing virtual destructor for VirtualMemoryAllocator

Fixes a warning from GCC 4.7.2.