Track return values of spy functions

src/core/base.js

@@ -56,11 +56,16 @@ getJasmineRequireObj().base = function(j$) {
       }),
       callTracker = new j$.CallTracker(),
       spy = function() {
-        callTracker.track({
+        var callData = {
           object: this,
           args: Array.prototype.slice.apply(arguments)
-        });
+        };
-        return spyStrategy.exec.apply(this, arguments);
+
+        callTracker.track(callData);
+        var returnValue = spyStrategy.exec.apply(this, arguments);
+        callData.returnValue = returnValue;
+
+        return returnValue;
       };
 
     for (var prop in originalFn) {