Cast was not needed since the return value was already being cast. Query
function changed to use heapq.nlargest() for simplicity

Problems fixed:
Replaced cmp: 1 instance in line 323 of search.py
Convert set() to {}: 3 instances in line 29 of MDP.py, line 181 and 215
of search.py
Convert .sort() to sorted(): 1 instance in line 150 of text.py
Cast map to list: 1 instance in line 47 of grid.py

Used tool 2to3 to finish the porting to Python 3 plus some fixes by
hand.