[Win32Debug] Stepping over breakpoint multiple times

Two problems are solved here. First is that current stepper was not deactivate when new one was created/nulled this is now done 100% at lines 915 and 930. This was causing incrementing F10 needed like picture displays:
![image](https://cloud.githubusercontent.com/assets/774791/2637126/9ddbacf6-be99-11e3-8c67-5ecab67e0c41.png)

Second problem when stepping with F10 and line where stepping will stop has breakpoint two events are triggered at same time by runtime currently only first one was handled. Now I check with HasQueuedCallbacks call if any other event is waiting after this if it is don't stop now but instead will let second one to handle stopping.

Bonus read:
http://blogs.msdn.com/b/jmstall/archive/2005/07/27/hasqueuedcallbacks.aspx