Added function: BM_face_create_ngon_vcloud
creating quads and tris use this too since it finds the best face winding direction based on surrounding face (if any)
* name bmesh operator func's BMO_slot_buffer_* rather then BMO_slot_* since it wasnt obvious some only dealt with buffer, some both.
* more typechecks and asserts of BMO_ functions (I lost some time calling a map with a buffer function that failed silently).
* small speedup for extrude check - test if the edge is wire _before_ doign a hash lookup.
when making a quad from 2 edges - it was comparing the edge lengths to avoid making a bowtie quad. but this doesnt work in all cases, now compare normals instead.
the problem was a triangle couldnt be made when there was a quad that used 3 of the verts.
* now check if overlapping face has same length as the one to be created.
* an unrelated fix - the output of a triangle was not being flagged by the bmesh_contextual_create operator.
On a place, Ctrl+T, Fkey would create a quad overlapping the 2 Tris.
Now this case is checked for in a general way - if the bounds of the face are already filled in with faces (that _only_ use these edges-verts), then dont create the face.
This is an option for the 'edgenet_fill' operator, since creating the face isnt incorrect, just not-what-you-want mostly.
added functions
* BM_edge_share_vert - returns shared vert between 2 edges.
* BM_face_exists_multi, BM_face_exists_multi_edge - check if existing faces fill the edge bounds.
* also add BM_ELEM_INTERNAL_TAG so low level functions can tag without conflicting with higher level functions that also rely on tagging elements.
* change BMO_elem_flag_* defines to inline functions.
* BMO_slot_map_insert() is too big for an inline function - un-inline it.
* remove redundant casts.
* added BM_elem_flag_set, BMO_elem_flag_set. to avoid 'if(...) enable(); else disable();' all over the place.
* added bmesh_operator_api_inline.c, the header file was getting messy.
