Info: Flushes all file buffers.
This does NOT update file length in a directory. To ensure a
file's length is correctly recorded, close the file via Fn 10H or
Notes: All MS-DOS tools that buffer I/O data will honor this function,
including the SmartDrv disk cache and caching performed by
Smartdrv perform its periodic disk output during a time-
critical program function, use Fn 0dH before starting that
Control does not return until all buffers have been flushed.
The default INT 23H Ctrl+Break handler calls this function when
DOS detects Ctrl+Break or Ctrl+C.