Rendering breaks when using end dates + dependencies

[salamanders]

This is an issue in the Gantt rendering widget, but could possibly be checked for in the ezgantt script (because the rendering widget does not give good advice on how to fix an issue)

If you have a task with a dependency and an end date, you have to make an assumption that the task will go from the end of the dependency to the end date. That assumption makes the gantt tool sad - it could span the entire time, or just the last day.

Recently we had a user that had to switch their (technically valid) list of end dates+dependencies to duration+dependencies.