adding backbone and underscore package overrides; adding underscore entry in registry.json

package-overrides/github/jashkenas/backbone@1.1.0.json

@@ -0,0 +1,10 @@
+{
+    "main": "backbone",
+    "dependencyShim": {
+        "backbone": ["jquery", "underscore"]
+    },
+    "dependencyMap": {
+        "jquery": "jquery@2.0.3",
+        "underscore": "underscore@1.5.2"
+    }
+}

package-overrides/github/jashkenas/underscore@1.5.2.json

@@ -0,0 +1,6 @@
+{
+    "main": "underscore",
+    "dependencyMap": {
+        "jquery": "jquery@2.0.3"
+    }
+}

registry.json

@@ -4,5 +4,6 @@
   "backbone": "github:jashkenas/backbone",
   "bootstrap": "github:twbs/bootstrap",
   "jquery": "github:components/jquery",
+  "underscore": "github:jashkenas/underscore",
   "webfont": "cdnjs:webfont/1.3.0#webfont"
 }