Revision 229756

MFC r209362, r210933, r228356:

r209362 (brian) [1]:
- Add a -t switch for masking output that's above or below certain
  thresholds.  This switch makes it a lot easier to locate problem
  areas when a process is threatening to consume all of your disk
  space.

r210933 (joel):
- Fix typos and spelling mistakes.

r228356 [2]:
- Update du(1):

  - Sort arguments alphabetically where appropriate
  - '-B blocksize' is not mutually exclusive of '-h|-k|-m'
  - Mention '-t' in synopsis
  - Other wording improvements
  - Update usage() output to reflect the new synopsis
  - Other miscellaneous improvements

Approved by:	brian [1]
PR:		162438 [2]