Some games (such as Digimon Survive) create temporary video files and
will hang if deleting them fails. Open the files with FILE_SHARE_DELETE,
which will allow this deletion to go ahead even if the FileSource hasn't
yet been closed.

Note that many windows codec packs do themselves open files without
FILE_SHARE_DELETE, so a similar hang can be observed in some windows
configurations.

I haven't checked that this is the file share mode used on windows
(alas, I don't have a windows machine available), so I haven't removed
the FIXME comment. Equally, I also updated the CreateFileW() call
in get_media_type(), but that _may_ be unnecessary.
Signed-off-by: David Gow <david@ingeniumdigital.com>