Add interval ignores accidentals

I found an inconsistency in the behavior of note input. It can lead to unexpected results.

• In note input mode, type e to insert an E, then down arrow to modify it to an E-flat.
• Type e again. It inserts another E-flat. That is sensible behavior. It's most likely what you want, and making you keep pressing down arrow to modify each note would be more work.
• Now add a chord by typing c then option-3. I would expect the chord to consist of C and E-flat, but instead it adds an E natural. The commands to add intervals don't pay attention to preceding accidentals the way the commands to insert individual notes do.