1. Did not replicate the annoying <beep> after an erroneous parameter (other
   OS/2 command line tools do not produce such beeps).
2. There's new sytnax for tree command (@todo: change oso*.txt!):

 tree [starting_dir] [/f]

 where starting_dir can be drive letter only (eg d:), or full path, where
 tree should start displaying directory structure
