To make the code more Python 3 compatible, I've made a few changes to how we handle keys() or iterkeys() calls on dictionaries. All functionality should remain the same.
* Remove the use of .keys() or .iterkeys() when iterating through a dictionary.
* Remove the use of .keys() when checking if key exists in dictionary.
* Replace dict.keys() with list(dict) to obtain a list of dictionary keys. In Python 3 dict.keys() returns a dict_keys object, not a list.
* Ensure all file descriptors are closed. Using the with statement ensures
closure.
* The main problem was with thousands of unclosed file desciptors from
tracker_icons mkstemp.
* Use a prefix 'deluge_ticon.' to identify created tracker_icon tmp files.
