Make sure the translucent background is available whenever possible

Now the Qt::WA_TranslucentBackground attribute is always set for the
mainwindow of konsole(regardless of whether compositing is available
when the window is created), just like in konsolepart.

I'm not 100% sure this approach is problem-free, but it works for me so
far under various environments and conditions. Do not hesihate to revert
it if you notice it causes big trouble.

src/MainWindow.cpp

@@ -58,23 +58,16 @@
 
 using namespace Konsole;
 
-static bool useTransparency()
-{
-    return KWindowSystem::compositingActive();
-}
-
 MainWindow::MainWindow()
     : KXmlGuiWindow()
     , _bookmarkHandler(0)
     , _pluggedController(0)
     , _menuBarInitialVisibilityApplied(false)
 {
-    if (useTransparency()) {
-        // It is userful to have translucent terminal area
-        setAttribute(Qt::WA_TranslucentBackground, true);
-        // But it is mostly annoying to have translucent menubar and tabbar
-        setAttribute(Qt::WA_NoSystemBackground, false);
-    }
+    // It is userful to have translucent terminal area
+    setAttribute(Qt::WA_TranslucentBackground, true);
+    // But it is mostly annoying to have translucent menubar and tabbar
+    setAttribute(Qt::WA_NoSystemBackground, false);
 
     // create actions for menus
     setupActions();

src/TerminalDisplay.cpp

@@ -593,7 +593,7 @@ void TerminalDisplay::drawBackground(QPainter& painter, const QRect& rect, const
 
     if (useOpacitySetting && !_wallpaper->isNull() &&
             _wallpaper->draw(painter, contentsRect)) {
-    } else if (WindowSystemInfo::HAVE_TRANSPARENCY && qAlpha(_blendColor) < 0xff && useOpacitySetting) {
+    } else if (qAlpha(_blendColor) < 0xff && useOpacitySetting) {
         QColor color(backgroundColor);
         color.setAlpha(qAlpha(_blendColor));