#2626 close? cancel! when two editor windows are running

[Jeremy Faden]

Sadie pointed out a nice bug with the editors, when you close a second window without saving. It properly gives the save/close/cancel dialog, but cancel doesn't always cancel for me, and for Sadie it never cancels, loosing her work.

1. start Autoplot with an editor
2. start a second Autoplot window with an editor
3. change the editor content without saving.
4. hit the "X" to close the window (File->Close may work too)
5. the save/close/cancel comes up, after the Autoplot GUI flashes off then back on for a moment.
6. hit cancel. For Sadie, the work is lost. (It was probably lost when the GUI didn't come back on.) For me, if the GUI didn't come back I've lost the work.

[Jeremy Faden]

The second Autoplot window was created in GuiSupport.newApplication, which for some reason would set the defaultCloseOperation to dispose. Only the AppManager can close a window. Also the requestClose operation now returns a boolean to confirm the close is okay, and only then are clean-up operations, like clearing the dom reference, done.