- bug fix, face center drawing was wrong for editmesh

- added several useful utility functions to editmesh,
   these can simplify/clarify a lot of mesh code, check them
   out
 - cleaned up EdgeSlide a bit to be clearer/shorter
     o bug fix, EdgeSlide did not always cancel correctly
     o bug fix, EdgeSlide did not choose initial "control" edge
       correctly after calc_meshverts_ext change

source/blender/src/editobject.c

@@ -2170,7 +2170,6 @@ void convertmenu(void)
 				Mesh *oldme= ob->data;
 				DispListMesh *dlm;
 				DerivedMesh *dm;
-				ModifierData *md;
 
 				basedel = base;