- Changed output of DocTestParser.get_program() to make it easier to

visually distinguish the expected output from the comments (use
  "##" to mark expected outputs, and "#" to mark comments).
- If the string given to DocTestParser.get_program() is indented, then
  strip its indentation.  (In particular, find the min indentation of
  non-blank lines, and strip that indentation from all lines.)