Fix Extension Manager bug: a poorly-scoped jQuery call causes it to see

*all* Bootstrap tabs in the entire DOM as part of its tab set, so it will
crash if any such other tabs exist in the UI.

This was the only jQuery call in the Extension Manager code that wasn't
scoped down to $dlg (or used an equivalent parent selector).

Author: peterflynn

src/extensibility/ExtensionManagerDialog.js

@@ -255,7 +255,7 @@ define(function (require, exports, module) {
             });
 
             // Update search UI before new tab is shown
-            $("a[data-toggle='tab']").each(function (index, tabElement) {
+            $("a[data-toggle='tab']", $dlg).each(function (index, tabElement) {
                 $(tabElement).on("show", function (event) {
                     _activeTabIndex = index;