- switch em_{vert,solid,wire}offs to be unsigned

- some other twiddles to fix mixed signedness compiler warnings

And from the "Dear lazy programmers" file: After you have extern declared
a variable 5 or more times at the top a function, you would have actually
saved a lot of effort by just putting it in the header where it belonged.
Or perhaps you thought by hiding it no one else would notice you were
using global variables to pass information around. Tsk tsk.

source/blender/src/drawobject.c

@@ -4080,7 +4080,6 @@ static int bbs_mesh_solid(Object *ob, DerivedMesh *dm, int facecol)
 
 void draw_object_backbufsel(Object *ob)
 {
-	extern int em_solidoffs, em_wireoffs, em_vertoffs;	// let linker solve it... from editmesh_mods.c 
 	int dmNeedsFree;
 	DerivedMesh *dm;