8.1.2 flag(xflag,xdata,low,high,mask_count,ii)

flag $<$ chanana $<$ BoaChanAna.f90

! NAM: flag  (sub)
! DES: set flag if data <low or >high 
! INP: 
!      low     = lower limit 
!      high    = upper limit
! OUT:
! HIS: FB040501  adapted from flag_pc