Windows binary builds: File -> Create + Copy defunct

[EagleTM]

Mentioned by rdymac on
https://bitcointalk.org/index.php?topic=325768.0
File -> Create/Restore and File -> Copy don't bring up a menu on Win builds. It works in native python on windows. File -> Open works on both

In gui/qt/main_window.py
my wild guess is in backup_wallet(self) and new_wallet(self)
QInputDialog.getText doesn't work with the win builds.

We could just use self.select_wallet_file() like we do for opening a file - however we may need extra code to make sure people are not destroying there existing wallets

[EagleTM]

I'd opt for using QFileDialog.getSaveFileName style of dialogue for Create and Copy

[ecdsa]

done