%N hisopen %F $MIR/src/subs/headio.c
%D Open the history file.
%P pjt
%: header-i/o
%B
FORTRAN call sequence:
        subroutine hisopen(tno,status)
        integer tno
        character status

  This opens the history file, and readies it to be read or written.

  Inputs:
    tno         The handle of the open data set.
    status      Either "read", "write" or "append".                     
