ocfs2: Handle O_DIRECT when writing to a refcounted cluster.

In case of writing to a refcounted cluster with O_DIRECT,
we need to fall back to buffer write. And when it is finished,
we need to flush the page and the journal as we did for other
O_DIRECT writes.

This patch fix oss bug 1191.
http://oss.oracle.com/bugzilla/show_bug.cgi?id=1191



Signed-off-by: Tao Ma <tao.ma@oracle.com>
Tested-by: Tristan Ye <tristan.ye@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>