Int 15 Fn 1E08  - Multidos Plus 4.01 - Set Context-switch Functions        [T]

   AX = 1E08h
   DX:BX -> context save handler
   DX:CX -> context restore handler

Note:  handlers may be removed by setting addresses to 0000h:0000h

Handlers are called with:
   ES:BX -> task's TCB

Return: all registers preserved