FIX: memory leak in the FileProcessor.
simplification of callback mechanism between FileProcessor and PendingFile (we do not need the added flexibility of Callbackable<> here)
Merge pull request #95 from reneme/fix_mem_leak

FIX: Memory leak in the FileProcessor.

PendingFile objects were created to keep track of file chunk uploads. Unfortunately they were not deleted properly afterwards.
This is a nasty bug since the deletion should happen when the PendingFile invokes it's callback, telling the FileProcessor that it is ready to be harvested and deleted. A deletion in the callback itself caused some nasty race conditions, though. My solution is, to save "completed PendingFiles" in a list and delete these list entries from time to time.