added #ds_internal_uri; removed #last_fixity_check (use fixity_checks.last); fixed oversight in ::find_by_last_fixity_check; added before_destroy callback and protected method
added #ds_internal_uri; removed #last_fixity_check (use fixity_checks.last); fixed oversight in ::find_by_last_fixity_check; added before_destroy callback and protected method

projecthydra-labs/fcrepo-admin,projecthydra-labs/fcrepo-admin