Mark keypad buttons as such in the input mapping screen

Both the slash key and the numpad slash key were displayed as 'Key /',
so it's not obvious to the user which key actually has been bound. Let's
display them as 'Key /' and 'KP /' instead. Same for other KP keys.

src/arch/InputHandler/InputHandler.cpp

@@ -128,6 +128,9 @@ RString InputHandler::GetDeviceSpecificInputString( const DeviceInput &di )
 
 	if( di.device == DEVICE_KEYBOARD )
 	{
+		if( di.button >= KEY_KP_C0 && di.button <= KEY_KP_ENTER )
+			return DeviceButtonToString( di.button );
+
 		wchar_t c = DeviceButtonToChar( di.button, false );
 		if( c && c != L' ' ) // Don't show "Key  " for space.
 			return InputDeviceToString( di.device ) + " " + Capitalize( WStringToRString(wstring()+c) );