Fix edge case for clamp_index() with any negative 'x' that is a
multiple of 'len', was returning 'len' which is invalid index.
Maybe the expression can be simplified back to a one-liner?
Now create the rotate edge in advance and copy its customdata (before joining the faces).
This commit also fixes an annoyance where tryangulating faces could create duplicate edges.
* 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.
* ntreeCompositExecTree accessed 'ntree' before NULL check.
* BM_face_triangulate accessed 'f' before NULL check.
also quiet warning in BKE_text_to_curve() and add a check for BMesh bridge loops so it knows quicker if it can copy loop data or not.
