Mirror in object mode. Works like Mirror in edit mode but only works on local axis (doing it differently would require a much more clever algorithm).
Mirror Object is assigned to Ctrl-M and I've add Ctrl-M to call Mirror Edit (on top of M alone) for practical reason. We should consider switching both to Ctrl-M for pratical reasons but I kept M for backward compatibility
Also added the menu and toolbox counterparts.
Minor addition to arithb.c: A function to print vectors to the console. Easier for debuging.