Fixed MSVC++ compile error due to sqrt() usage.

cockatrice/src/arrowitem.cpp

@@ -66,7 +66,7 @@ void ArrowItem::updatePath(const QPointF &endPoint)
 {
     const double arrowWidth = 15.0;
     const double headWidth = 40.0;
-    const double headLength = headWidth / sqrt(2);
+    const double headLength = headWidth / pow(2, 0.5); // aka headWidth / sqrt (2) but this produces a compile error with MSVC++
     const double phi = 15;
     
     if (!startItem)

cockatrice/src/playertarget.cpp

@@ -90,7 +90,8 @@ void PlayerTarget::paint(QPainter *painter, const QStyleOptionGraphicsItem * /*o
         cachedPixmap = QPixmap(translatedSize.width(), translatedSize.height());
         
         QPainter tempPainter(&cachedPixmap);
-        QRadialGradient grad(translatedRect.center(), sqrt(translatedSize.width() * translatedSize.width() + translatedSize.height() * translatedSize.height()) / 2);
+	// pow(foo, 0.5) equals to sqrt(foo), but using sqrt(foo) in this context will produce a compile error with MSVC++
+        QRadialGradient grad(translatedRect.center(), pow(translatedSize.width() * translatedSize.width() + translatedSize.height() * translatedSize.height(), 0.5) / 2);
         grad.setColorAt(1, Qt::black);
         grad.setColorAt(0, QColor(180, 180, 180));
         tempPainter.fillRect(QRectF(0, 0, translatedSize.width(), translatedSize.height()), grad);