Blender Git Loki

Fix T55490, intersect two triangles fails.

Need to use the 'use_partial_connect' option in island connect,
so changed signatures of various functions to pass that into and
then down from BM_mesh_intersect (making true for intersect, false
for boolean).
Then fix bm_face_split_edgenet_partial_connect to work when
input edges are not necessarily wire, but at least not in the
face they are being connected in. That caused generalization
of core BM_vert_separate_hflag_wire (which is only used in
this one place in all Blender).