div_factor has been implemented for two times, cleanup it.
And I move them into a independent file named math.h because they are
common math functions.
[Eric Sandeen: port kernel commit 3fed40c to userspace]
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
