SwNtfy Fn 0003H: Switcher Is Activating Your Session

  Expect: AX    0003H
          BX    ID of the session that is about to be activated
          CX    flags: 0001H=this is a new session
                       0000H=resuming a previously-suspended session
          ES:DI addr of switcher's service-entry address
  Return: AX    0000H (you must return 0 in all cases)
    Info: Task switchers call this to let you know that a new session is
          about to be started or that a suspended session is about to be
          resumed.  When a session is resumed, this is called only after
          all instance data and the session's interrupt table has been

          When called, interrupts are disabled you should NOT enable
          interrupts or use any DOS fns.

       BX will contain the session ID of the session that is about to be
          activated.  Global TSRs may wish to keep track of new sessions if
          they take special actions for each session.  You can identify a
          new session by bit 0 of the value in CX.

    ES:SI will contain the task switcher's service entry address.  Use this
          address if you need to call any task-switcher service fns.

  Return: AX=0000H (must be 0)

   Notes: For new sessions, this will be preceded by a SwNtfyFn 0005H
          (create session).

See Also: Switcher Services and Notifications
          INT 2fH 4bxxH (switcher functions)