writev and aio_write to flush properly.

This is Christoph's patch merged with the new nobrl file operations
Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>

From: Christoph Hellwig <hch@lst.de>

 - support vectored and async aio ops unconditionally - this is above
   the pagecache and transparent to the fs
 - remove cifs_read_wrapper.  it was only doing silly checks and
   calling generic_file_write in all cases.
 - use do_sync_read/do_sync_write as read/write operations.  They call
   ->readv/->writev which we now always implemente.
 - add the filemap_fdatawrite calls to writev/aio_write which were
   missing previously compared to plain write.  no idea what the point
   behind them is, but let's be consistent at least..
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Steven French <sfrench@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>