INT 2F - MS WINDOWS, DPMI, various - RELEASE CURRENT VIRTUAL MACHINE TIME-SLICE
        AX = 1680h
Return: AL = 00h if the call is supported
        AL = 80h (unchanged) if the call is not supported
Notes:  programs can use this function in idle loops to enhance performance
          under multitaskers; this call is supported by MS Windows 3.0, DOS 5+,
          DPMI 1.0+, and will be supported in OS/2 2.0 for multitasking DOS
          applications
        does not block the program; it just gives up the remainder of the time
          slice
        should not be used by Windows-specific programs
SeeAlso: INT 15/AX=5305h,INT 21/AH=89h,INT 7A/BX=000Ah