Directories were getting added to the data_seq index. It might have
looked like they weren't because their data_seqs were always 0 but when
inodes are created they don't have 'have_item' set so all the fields are
added regardless of their current value.
We'd rather not have to wade their directories when looking for regular
file data in the data_seq index so let's explicitly test for regular
files when updating the data_seq index items.
Signed-off-by: Zach Brown <zab@versity.com>