Re-add Mock Clock behavior as global 'clock'

- Use clock.install, clock.tick...
- Add unit coverage.
- Fixes old bug in function scheduler

lib/jasmine-core/boot/boot.js

@@ -38,6 +38,9 @@
       return env.spyOn(obj, methodName);
     },
 
+    clock: function() {
+      return env.clock;
+    },
 
     jsApiReporter: new jasmine.JsApiReporter(jasmine)
   };