fix for BM_faces_join_pair() making the assumption that only the 2 faces use an edge, face winding could be flipped incorrectly.

also remove search for shared edges - all callers pass the edge in.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60943 954f8c5b-7b00-dc11-b283-0030488c597c