Saving a child node wipes out the end time

The current version of the code sets the end time of the event by adding a number of seconds to the date array['seconds'] element. I'm not sure if it's because the date form fields do not include seconds, or if it's because the resulting number of seconds is usually >60, but the Date API is ignoring this number, and I end up with an end time that is the same as the start time.

So I reworked the code to correctly use the value the user enters as the end time. See the attached patch.