Merge pull request #1563 from minrk/clear_output clear_output improvements, which allow things like progress bars and other simple animations to work well in the notebook. * `clear_output()` clears the line, even in terminal IPython, the QtConsole and plain Python as well, by printing `\r` to streams. * `clear_output()` avoids the flicker in the notebook by adding a delay, and firing immediately upon the next actual display message. * `display_javascript` hides its `output_area` element, so using display to run a bunch of javascript doesn't result in ever-growing vertical space.