When writing less than a filesystem block of data into an unwritten extent
via buffered I/O, __xfs_get_blocks fails to set the buffer new flag. As a
result, the generic code will not zero either edge of the block resulting
in garbage being written to disk either side of the real data. Set the
buffer new state on bufferd writes to unwritten extents to ensure that
zeroing occurs.

SGI-PV: 960328
SGI-Modid: xfs-linux-melb:xfs-kern:28000a
Signed-off-by: NDavid Chinner <dgc@sgi.com>
Signed-off-by: NLachlan McIlroy <lachlan@sgi.com>
Signed-off-by: NTim Shimmin <tes@sgi.com>