[FIX] WPropertyObserver was missing a SPtr convenience type, but...

[FIX] WPropertyObserver was missing a SPtr convenience type, but WCondition::SPtr (base class) was used instead.

src/core/common/WPropertyObserver.h

@@ -49,6 +49,11 @@ public:
      */
     typedef std::map< std::string, boost::shared_ptr< WPropertyBase > > PropertyNameMap;
 
+    /**
+     * Convenience type for a shared pointer on property observers.
+     */
+    typedef boost::shared_ptr< WPropertyObserver > SPtr;
+
     /**
      * Default constructor.
      */