The current code for calendar and the classhelp "widgets" can change
an input field, but they don't trigger the field's onchange
event.

http://stackoverflow.com/questions/2856513/trigger-onchange-event-manually

recommends one method by adding:

if ("fireEvent" in element)
    element.fireEvent("onchange");
else
{
    var evt = document.createEvent("HTMLEvents");
    evt.initEvent("change", false, true);
    element.dispatchEvent(evt);
}

to force the function that does the change to the field to trigger
the onchange event. This should probably be done in pure javascript
and not reply on any particular javascript libs like jQuery.

I noticed this because the templates I am designing have onchange
events that change the background color of the label to indicate that
the form has been changed so people don't forget to commit their changes.

Sounds like a good idea. 
If you cannot think of any drawbacks, just commit something for it.

I used slightly different code (the then and else cases are flipped).
Committed as: e8b3d3a14563

The helper popups could use some work. There is code that has the same
function, but that are named differently. Some code is inlined in the
html page, some calls function in an external .js library.

But that is for another day.