    CHNGDO reads a syntactically correct EXTENDED FORTRAN program
(through F:111) and changes DO statements to prevent zero trip loops
so the program will produce same results on CP-6 ANSFORT as EXTENDED
FORTRAN did.  In other words, make all DO statements make at least one
pass though the loop even if terminating condition is satisfied
on the initial pass.  For instance, the statement:
   DO 99 I=1,J
would be changed by CHNGDO to:
   DO 99 I=1,MAX(1,J)

Sample run:
   !SET F:111/extended-fortran-source
   !SET F:112/cp6-ansfort-source;OUT
   !SET F:108 ME
   !CHNGDO.

NOTES:
  1)  CHNGDO reads through F:111, writes the changed program through
      F:112 and echoes the before and after DO statements through
      F:108.  The ';OUT' must be included on the F:112 SET as in sample
      above.

  2)  Programs which run correctly on CP-V ANSFORT should NOT be run
      through this program because CP-V ANSFORT supports zero trip
      DO statements the same as CP-6.

  3)  CHNGDO will NOT detect the following condition properly:
        BEG= 80
        END= 1
        INCR= -1
        DO 99 I=BEG,END,INCR
      CHNGDO will change it to:
        DO 99 I=BEG,MAX(BEG,END),INCR
      when it should be:
        DO 99 I=BEG,MIN(BEG,END),INCR

  4)  CHNGDO will NOT handle continued DO statements

  5)  CHNGDO will not change a statement whose parameters are all
      numeric(Ex: DO 99 I=1,80,2)

  6)  CHNGDO will NOT change implied DO statements.
