Memory leak fix

Hello!
I started to use RoboSpice library in my project and I liked its design and usability very much.
But I have faced a problem: when I execute many similar requests, I have a great memory leak after them. After investigating this problem I have found that memory leak is in mapPendingRequestToRequestListener field in SpiceManager class. Some listeners are not removed from this map. It is so because this field is IdentityHashMap, but remove method is called only for one of aggregated requests. So I changed code a little to remove all listeners after execution.