INT 2fH 4a11H BX=0000H: Get Dblspace Version & Drives

                                                         Compatibility: 6.0+ 
 Expects: AX    4a11H (mux number)
          BX    0000H (DoubleSpace fn code)
 Returns: AX    DoubleSpace API Error Code (0000H=success)
          BX    444dH signature; 'M','D')
          CL    first drive letter used by DoubleSpace (41H='A', etc.)
          CH    count of drives letters used by DoubleSpace
          DX    Version number (an internal code) high bit indicates current
                code location (high or low memory)
    Info: You may use this fn to see if DoubleSpace is installed and to
          obtain the range of drive letters that it uses.

       CL is the ASCII code for a drive letter (for instance, 45H=E).
       CH is a count of how many drive IDs are controlled by DoubleSpace;
          for instance, CX=0544H means drives D,E,F,G, and H are available
          to DoubleSpace for use as drive IDs.

       DX The low 15 bits identify the version number (this shows up as
          0006H on my PC).

          Bit 15 is a location flag:  When set, it indicates that
          DBLSPACE.BIN is not at its final location (for instance, the
          DEVICEHIGH=DBLSPACE.SYS command is not in CONFIG.SYS or has not
          been executed yet.

See Also: DoubleSpace Overview
          DoubleSpace API
          INT 2fH: Multiplex Interrupt
          DOS Functions