Calls the AbortIO vector of the appropriate device to stop an
asynchronously started io request before completion. This may
or may not be done. You still have to do a WaitIO() on the
iorequest structure.
INPUTS
iORequest
Pointer to iorequest structure.
RESULT
Errorcode if the abort request failed, 0 if the abort request went
well. io_Error will then be set to IOERR_ABORTED.