BBN-V6/doc/ipc/ports_how

1. Define a new flag bit FPORT in file.h with some previously unused
bit value.

2. In closef() in fio.c, change
        if(rfp->f_count <= 1)
                closei(rfp->f_inode, rfp->f_flag&FWRITE);
to
        if(rfp->f_count <= 1) {
                /* Next 3 lines are Rand addition for ports - jsz, 3/76 */
                if (rfp->f_flag&FPORT)
                        portclose(rfp);
                else
                        closei(rfp->f_inode, rfp->f_flag&FWRITE);
        }

3. In seek() in sys2.c, change the check for FPIPE to (FPIPE|FPORT).

4. In cdevsw[] in c.c, add an entry like
/* 18*/ &portopen, &nodev,    &portread, &portwrite,&portstty,  /* ports */

5. In sysent[] in sysent.c, add an entry like
        2, &port,                       /* 59 = port (rand:jsz) */

6. Include the ports driver, which I am sending as a separate message.

7. Put port.s, which I am sending as a separate message, in the library.