accessing dereferenced file objects

[Hartmut Birr]

Hi,

looking through our file functions, we do always access a file object
after it was dereferenced by the completion routine and if the
FO_SYNCHRONOUS_IO flag is set. If FO_SYNCHRONOUS_IO is set, the
completion routine should not dereference the file object or we have to
add an additional reference. If FO_SYNCHRONOUS_IO is set, we have also
to dereference the file object after calling the driver.

- Hartmut