Don't focus to the tab which is going to be removed.

This fixes #569. In the previous revision, onTabClose method tried to focus to the first child even if it was going to be closed as a member of closing tree. Then TabSelect event was unexpectedly fired, TabWindow.prototype.handleEven (defined in resource:///modules/WindowsPreviewPerTab.jsm) raised an error, and blocked all following event handlers for TabSelect event. As the result, cached tabs list were not cleared and Ctrl-Tab feature was killed.

modules/browser.js

@@ -3049,6 +3049,9 @@ TreeStyleTabBrowser.prototype = {
 		if (nextFocusedTab && toBeClosedTabs.indexOf(nextFocusedTab) > -1)
 			nextFocusedTab = this.getNextFocusedTab(nextFocusedTab);
 
+		if (nextFocusedTab && nextFocusedTab.hasAttribute(this.kREMOVED))
+			nextFocusedTab = null;
+
 		this._reserveCloseRelatedTabs(toBeClosedTabs);
 
 		this.detachTab(tab, { dontUpdateIndent : true });