Bring a little more compability with GNU units 2.12

• notionally support a 'history file' flag. This doesn't do much now, but is there to prevent scripts written against GNU units from breaking
• correctly gracefully quit rather than exit (this will make it easier to support a history file in the future)
• remove the "t" flag from fopen which was there to support windows. We have not supported windows since at the latest, the introduction of capsicum.