Log Message:
Update pbzip2 to 1.1.18.

Changes in 1.1.18:
- Fixed bug of metadata unpreserved on empty files compress (bug #1011021)

Changes in 1.1.17:
- Fixed refusal to write to stdout on -dc from stdin (bug #886628)
- Fixed occasional failure on decompress with --ignore-trailing-garbage=1
  with multiple bad blocks in the archive (bug #886625)

Changes in 1.1.16:
- Fixed bug - deadlock due to unsynchronized broadcasts (bug #876686)
- Prevent deletion of input files on error (bug #874543)
- Document how to compress/decompress from standard input (bug #820525)
- Added more detailed kernel error messages (bug #874605)
- Fixes for error handling in muliti-file processing (bug #883782)