Moved Object.Join() into a function of an object.

eg.
ret_val = ob.join(objects)
Now it dosent depend on the current selection, or change the selection context.

Made respective join_* functions return 0 if the join was not mode, 1 when it workes.

source/blender/include/BIF_meshtools.h

@@ -35,7 +35,7 @@
 
 struct Object;
 
-extern void join_mesh(void);
+extern int join_mesh(void);
 
 extern void fasterdraw(void);
 extern void slowerdraw(void);