Widespread random code cleanup.

Most of this code was old enough to vote.  Examples of cleanups:

+ Backslashes were used for line continuation even inside unclosed
  bracket structures, from back in the days that was still needed.

+ There was no use of % formats, and e.g. the old fpformat module was
  still used to format floats "by hand" in conjunction with rjust().

+ There was even use of a do-nothing .ignore() method to tack on to the
  end of a chain of method calls, else way back when Python would print
  the non-None result (as it does now in an interactive session -- it
  *used* to do that in batch mode too).

+ Perhaps controversial (although I can't imagine why for real <wink>),
  used augmented assignment where helpful.  Stuff like

      self.total_calls = self.total_calls + other.total_calls

  is just plain harder to follow than

      self.total_calls += other.total_calls