qt: don't pass BitcoinGUI to bringToFront()

The main window (BitcoinGUI) does not need to be passed to
bringToFront(), doing so sets Qt::WindowStaysOnTopHint on the main
window and causes it to flicker.

Fixes #903.

Author: diegoviola

src/qt/bitcoingui.cpp

@@ -1511,7 +1511,7 @@ void BitcoinGUI::showNormalIfMinimized(bool fToggleHidden)
     if (!isHidden() && !isMinimized() && !GUIUtil::isObscured(this) && fToggleHidden) {
         hide();
     } else {
-        GUIUtil::bringToFront(this);
+        show();
     }
 }