getDebugInfo tweaks

[rwjblue]

After playing around with .getDebugInfo() a bit, I'd like to see a few changes:

• Better output when calling .getDebugInfo() where Ember.run.backburner.DEBUG is not set. Perhaps even returning the data that we do have (which is essentially everything except the stacks).
• When the scheduled timers are scheduled to fire (essentially executeAt info).
• Are we flushing currently?
• Is the current flush due to an autorun?
• Is a future autorun scheduled? Adding autorun stack to debug info #361

[rwjblue]

/cc @scalvert

[scalvert]

Seems reasonable.

I'm torn about

Better output when calling .getDebugInfo() where Ember.run.backburner.DEBUG is not set

(and thought about this when I was implementing) because would one expect to get debug info when not in DEBUG mode? If we go that route, we may want to think about different naming for this.