Fix krazy issues: Use explicit constructors

* Fix all warnings about non-explicit constructors except for those
   in 3rdparty code.

src/libs/aggregation/examples/text/main.h

@@ -42,7 +42,7 @@ class MyMain : public QWidget
     Q_OBJECT
 
 public:
-    MyMain(QWidget *parent = 0, Qt::WFlags flags = 0);
+    explicit MyMain(QWidget *parent = 0, Qt::WFlags flags = 0);
     ~MyMain();
 
     void add(IComboEntry *obj);