majalan

Copperbox revision 2946.

Initial work on symbolic stretch. Because events are parametric on onset we would want  let dblevt = stretch 2.0 evt1 to double the length of evt1 but allow us to place dblevt at arbitrary positions - i.e. we don't want to stretch onset as well as duration, so we need a symbolic stretch rather than an affine one.

Unfortunately symbolic stretch seems complicated as Majalan's events may return answers that represent positions and need stretching themselves.