Blender Git Loki

Fix for particle shape key editing to prevent losing shape data
when switching the active key.

Particle shapes were always using the relative blending of keys when
evaluating hair data. This works ok for meshes, because their edit data
is entirely separate from the mesh data (using bmesh). For particles,
however, the edit mode is hardwired to the hair data, so when switching
keys in edit mode we must take care to replace everything with the
shape. Otherwise the hair data will be using blender shapes and the edit
data will overwrite any shape keys with that.