SUBROUTINE KNADD(IK)
 
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
C   Add a slot for a new particle in the KN list. No info is stored.
C
C *IK        Integer variable (write)
C            KN track number returned to caller. 0 if error or overflow.
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>