[Qt] misc small Mac related changes/cleanups

- cleanup Info.plist.in and specify high DPI mode enable command as per
  http://blog.qt.digia.com/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11/
- move setting of QApplication::setAttribute() to bitcoin.cpp and add
  attribute for enabling use of high DPI pixmaps for Qt >= 5.1
- add missing setWindowTitle() on Mac
- cleanup Mac / non-Mac setup in bitcoingui.cpp

src/qt/bitcoin.cpp

@@ -200,6 +200,13 @@ int main(int argc, char *argv[])
 
     Q_INIT_RESOURCE(bitcoin);
     QApplication app(argc, argv);
+#if QT_VERSION > 0x050100
+    // Generate high-dpi pixmaps
+    QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+#endif
+#ifdef Q_OS_MAC
+    QApplication::setAttribute(Qt::AA_DontShowIconsInMenus);
+#endif
 
     // Register meta types used for QMetaObject::invokeMethod
     qRegisterMetaType< bool* >();

src/qt/bitcoingui.cpp

@@ -69,28 +69,32 @@ BitcoinGUI::BitcoinGUI(bool fIsTestnet, QWidget *parent) :
 {
     GUIUtil::restoreWindowGeometry("nWindow", QSize(850, 550), this);
 
-#ifndef Q_OS_MAC
     if (!fIsTestnet)
     {
         setWindowTitle(tr("Bitcoin") + " - " + tr("Wallet"));
+#ifndef Q_OS_MAC
         QApplication::setWindowIcon(QIcon(":icons/bitcoin"));
         setWindowIcon(QIcon(":icons/bitcoin"));
+#else
+        MacDockIconHandler::instance()->setIcon(QIcon(":icons/bitcoin"));
+#endif
     }
     else
     {
         setWindowTitle(tr("Bitcoin") + " - " + tr("Wallet") + " " + tr("[testnet]"));
+#ifndef Q_OS_MAC
         QApplication::setWindowIcon(QIcon(":icons/bitcoin_testnet"));
         setWindowIcon(QIcon(":icons/bitcoin_testnet"));
-    }
 #else
-    setUnifiedTitleAndToolBarOnMac(true);
-    QApplication::setAttribute(Qt::AA_DontShowIconsInMenus);
-
-    if (!fIsTestnet)
-        MacDockIconHandler::instance()->setIcon(QIcon(":icons/bitcoin"));
-    else
         MacDockIconHandler::instance()->setIcon(QIcon(":icons/bitcoin_testnet"));
 #endif
+    }
+
+#if defined(Q_OS_MAC) && QT_VERSION < 0x050000
+    // This property is not implemented in Qt 5. Setting it has no effect.
+    // A replacement API (QtMacUnifiedToolBar) is available in QtMacExtras.
+    setUnifiedTitleAndToolBarOnMac(true);
+#endif
 
     // Create wallet frame and make it the central widget
     walletFrame = new WalletFrame(this);