GitLab

- Add support for computing CRC-16 value.
- Add call to check/verify/set csum on block_groups.
- Add a test program to verify csum operations.
Signed-off-by: Jose R. Santos <jrs@us.ibm.com>
Signed-off-by: Andreas Dilger <adilger@clusterfs.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>