PEG vobcoorder_isActive--tjl: Add isActive into VobCoorder

One more method for VobCoorder, for querying activity of a cs.

Issues

System Message: ERROR/3 (../ffdoc/libvob/pegboard/vobcoorder_isActive--tjl/peg.rst, line 13)

Section empty; must have contents.

Add into VobCoorder:

/** Whether activate(cs) has been called.
 */
public boolean isActive(int cs);