Parallel copy for unaligned DIO has an unpleasant interaction with AIO - Since AIO is async, we must do the copying first.

This shows up as rare failures in 119i, which tests unaligned AIO.

Handling this correctly for AIO introduces some complexity, so instead I would like to disable unaligned AIO.  AIO is rarely used and if there's a real desire for unaligned AIO, we can fix this by adding an additional wait for the data to be copied.  But I think this is a very small use case and we can just disable it instead.