[MonoDevelop] Stripped down GTK# notebook tabs for monodevelop

[Adam Tauno Williams]

>> Andrés: I think that's a pretty neat idea, to have the icon and close button
>> on the active tab and removed on the other tabs.
>I disagree.  If this is implemented, please provide an option to turn it off.
>I'll frequently hop from file to file during development and then
>eventually clean up the open windows by closing ones I'm not using
>anymore.  

Ditto.