CCEditBox的bug修正

在ios平台上，CCEditBox的输入框对焦点有误，修改了代码重新计算了实际对焦位置。

void CCEditBoxImplIOS::setPosition(const CCPoint& pos)
{
    //TODO should consider anchor point, the default value is (0.5, 0,5)
    //[GET_IMPL setPosition:convertDesignCoordToScreenCoord(ccp(pos.x-m_tContentSize.width/2, pos.y+m_tContentSize.height/2))];
    CCPoint anchorPoint;
    if (m_pEditBox->isIgnoreAnchorPointForPosition()) {
        anchorPoint = CCPointZero;
    }
    else
    {
        anchorPoint = m_pEditBox->getAnchorPoint();
    }
    CCPoint textPoint = ccp(- m_tContentSize.width*anchorPoint.x, m_tContentSize.height*(1-anchorPoint.y));
    CCPoint worldPos = m_pEditBox->convertToWorldSpace(textPoint);
    [GET_IMPL setPosition:convertDesignCoordToScreenCoord(worldPos)];
}