AboutBox is not modal

[Jorgen Bodde]

Hi all,

I noticed that the wx.AboutBox isn't shown modal. This is really not
desired as you would expect people to close the dialog and continue
with the app not that they can continue working while the about box is
open.

This is on Ubuntu with wxPython 2.8.6.1 and can be seen in the
wxPython demo as well.

Regards,
- Jorgen