Makes the given card active. Makes it the visible card in the TabPanel's CardLayout and highlights the Tab.
@param {String/Number/Ext.Component} card The card to make active. Either an ID, index or the component itself.
@return {Ext.Component} The resulting active child Component. The call may have been vetoed, or otherwise
modified by an event listener.
function(card) {
        var me = this,
            previous;

        card = me.getComponent(card);
        if (card) {
            previous = me.getActiveTab();

            if (previous !== card && me.fireEvent('beforetabchange', me, card, previous) === false) {
                return false;
            }

            // We may be passed a config object, so add it.
            // Without doing a layout!
            if (!card.isComponent) {
                Ext.suspendLayouts();
                card = me.add(card);
                Ext.resumeLayouts();
            }

            // MUST set the activeTab first so that the machinery which listens for show doesn't
            // think that the show is "driving" the activation and attempt to recurse into here.
            me.activeTab = card;

            // Attempt to switch to the requested card. Suspend layouts because if that was successful
            // we have to also update the active tab in the tab bar which is another layout operation
            // and we must coalesce them.
            Ext.suspendLayouts();
            me.layout.setActiveItem(card);

            // Read the result of the card layout. Events dear boy, events!
            card = me.activeTab = me.layout.getActiveItem();

            // Card switch was not vetoed by an event listener
            if (card && card !== previous) {

                // Update the active tab in the tab bar and resume layouts.
                me.tabBar.setActiveTab(card.tab);
                Ext.resumeLayouts(true);

                // previous will be undefined or this.activeTab at instantiation
                if (previous !== card) {
                    me.fireEvent('tabchange', me, card, previous);
                }
            }
            // Card switch was vetoed by an event listener. Resume layouts (Nothing should have changed on a veto).
            else {
                Ext.resumeLayouts(true);
            }
            return card;
        }
    }