The bmo_extrude_vert_indiv_exec was removing the MVERT_SKIN_ROOT
flag on the original vertices resulting in moving the skin root to the last
extruded vertex. Note that this is inconsistent with
bmo_extrude_edge_only_exec and bmo_extrude_face_region_exec which
will remove the flag on the extruded vertices.
The fix changes bmo_extrude_vert_indiv_exec so that the flag is
removed on the duplicated vetex.