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.
* made bmesh_structure.h function names more consistant.
* remove unused code in bmesh_structure.c
* removed 'Edge Flip' operator (missing from bmesh but looked into trunk feature and dont think its worth keeping).
* tagged some BMESH_TODO's
* better type safety for BM_elem_flag_* and BM_elem_index_* functions.
* add BMElem type to be used where BMFace/Edge/Vert/Loop can be interchanged.
* fix bug in select manifold, found when making functions more strict.
* 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.
