Remain keep unread stories against Mark ALL As Read 

Now `mark_all_as_read` button works like google reader.

If I check some stories `keep_read`, and do `mark_all_as_read`
the stories will turn into unread... yes, ALL as read

That's correct.

But I think 
`keep_unread` should work stronger than `mark_all_as_read` .
I except to remain them as unread.