* combine: Man page improvements, to clarify even more that order does

* combine: Man page improvements, to clarify even more that order does
  matter and that the operations are not commutative. Closes: #361123
* combine: The behavior of "or" was fairly strange if lines were repeated in
  a file. Changed behavior to just print all lines from both files, even
  if this means printing dups. Not sure I like this behavior either, but
  it's consistent with the very useful behaviors of "and" and "not".