Fixed warning regarding virtual function overrides. Using C++ standard.

See http://msdn.microsoft.com/en-us/library/bb384874(v=vs.90).aspx

cockatrice/src/decklistmodel.h

@@ -19,7 +19,7 @@ public:
     int getNumber() const { return dataNode->getNumber(); }
     void setNumber(int _number) { dataNode->setNumber(_number); }
         float getPrice() const { return dataNode->getPrice(); }
-        void setPrice(float _price) { dataNode->setPrice(_price); }
+    void setPrice(const float _price) { dataNode->setPrice(_price); }
     QString getName() const { return dataNode->getName(); }
     void setName(const QString &_name) { dataNode->setName(_name); }
     DecklistCardNode *getDataNode() const { return dataNode; }

common/decklist.h

@@ -83,7 +83,7 @@ public:
 	virtual QString getName() const = 0;
 	virtual void setName(const QString &_name) = 0;
         virtual float getPrice() const = 0;
-        virtual void setPrice(float _price) = 0;
+        virtual void setPrice(const float _price) = 0;
         float getTotalPrice() const { return getNumber() * getPrice(); }
 	int height() const { return 0; }
 	bool compare(AbstractDecklistNode *other) const;