Blender Git Loki

Fix for bug #5319, multiresolution mesh - inconsistent hide behavior

Multires operations now pay attention to vertex flags, so both selection and
hiding are propagated up and down the levels.

Note: only the lowest level of detail for vertex flags is retained when
switching levels. E.g., after selecting vertices at the highest level, then
switching to the lowest level, then back to the highest level, the vertex
selection will have changed. (This is a potentially fixable issue.)