cmfs-tools: code clean up and minor fixes

This patch contains several code cleanup and minor fixes, which make
mkfs.cmfs really works, the changes include,
- fix typo in libcmfs/cmfs_err.et, now error info corrected to "Unsupported feature(s) found"
- remove orphan_dir item in system_files[], because we remove this item
  from system inode index.
- add help info in usage()
- correct getopt_long parameters in get_state, by the information in
  usage()
- remove several fprintf debug info lines.
- implement feature_skip(), if nojournal specified, skip journal inode.