INT 2fH 4B03H: Allocate Switcher ID

                                                         Compatibility: 5.0+ 
 Expects: AX    4B03H  (INT 2fH)
          BX    0000H
          ES:DI Service-function address of task switcher to allocate
 Returns: AX    0000H if successful (if a switcher ID is available
          BX    switcher ID for caller (if successful)
    Info: Programs which wish to act as a task switcher (or session
          manager) must obtain a switcher ID.  That ID will be in the range
          0000h-000fH; it will used as the high four bits in the task IDs
          it creates for tasks it handles.

          The first task switcher loaded must intercept this fn and provide
          this service (you know you're the first when INT 2fH 4B02H
          returns AX=0000h).

          This in NOT called by normal application programs--only by task

See Also: INT 2fH 4BxxH: Task Switcher Functions
          Switcher Services and Notifications
          INT 2fH: Multiplex Interrupt
          DOS Functions