TST: QApplication doesn't quit early enough with PySide.

[punchagan]

Fixes #1628. This commits adds a check in tests, to see if there's
already a QApplication and use it, instead of creating a new one each
time.

[fperez]

Great, thanks for the quick reply @punchagan! I'll leave it to @jdmarch and you guys to test this one, since I'm not using pyside. @minrk also saw the breakage, so he might want to pitch in.

[jdmarch]

Looks good. Broken qtconsole tests now pass with pyside 1.1.0-2 and pyqt on WinXP, Win7, and OSX 10.6.

[fperez]

Great, thanks. If you want to merge, go ahead... Quick summary of tips for merging:

• use the "Merge pull request" button.
• in the blue area, start by copy/pasting the description from the top of the PR. That's typically a good message for the whole PR, though you want to edit it manually to read better, add any other info from the discussion, remove unnecessary detail, etc. But it's a good start.
• to copy the PR message, click on 'edit' at the top, so you can copy the raw markdown instead of the rendered text. That will make things like bullet lists read better in text.
• don't forget to add at the end "Closes #NN, closes #mm,..." for any tickets the PR may close.

I'd rather you get the swing of it so we can better scale this process :)