Docview and IDE patch from Morag Hua with fix for bug #1217890

Docview and IDE patch from Morag Hua with fix for bug #1217890
"Closing view crashes Python" plus some new features:

    New feature added to the IDE is 'Extensions'.  Under
    Tools|Options|Extensions, you can add calls to external programs.
    For example you can add a "Notepad" extension (under windows) that
    will exec Notepad on the currently open file.  A new "Notepad"
    menu item will appear under the Tools menu.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@34638 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775