Zenmap uses the wrong clipboard on Windows

Reports:
- http://seclists.org/nmap-dev/2016/q1/116
- http://seclists.org/nmap-dev/2016/q1/59
- http://seclists.org/nmap-dev/2015/q4/229

Python GTK can use [several clipboards](http://www.pygtk.org/pygtk2reference/class-gtkclipboard.html), but Windows only uses the CLIPBOARD one. Need to figure out how to enforce the use of the correct one.
