hammer2 - Make the CRC check code programmable

hammer2 - Make the CRC check code programmable

* Add infrastructure to allow a CRC check code method request to be stored
  in an inode.  The method will be inherited by anything created under the
  inode.

* Refactor the check_algo and comp_algo encoding to make the distinction
  between the requests in ipdata fields and the actual specification stored
  in bref.methods.

* Make sure that the hidden directory inherits the iroot's algorithm
  specifications for consistency.