Changed Window::requestFocus() return type from bool to void

Reasons:
* Consistent with other sf::Window methods
* User can test whether focus succeeded by subsequent hasFocus() call
* Implementation would have to call hasFocus() anyway on some systems

Also: minor code style change in Window::hasFocus()

include/SFML/Window/Window.hpp

@@ -423,11 +423,10 @@ public:
     /// is free to deny the request.
     /// This is not to be confused with setActive().
     ///
-    /// \return True if operation was successful, false otherwise
     /// \see hasFocus
     ///
     ////////////////////////////////////////////////////////////
-    bool requestFocus();
+    void requestFocus();
 
     ////////////////////////////////////////////////////////////
     /// \brief Check whether the window has the input focus