PEP8 format {betweenness,mst,test_weighted,weighted}.py with automation
Handle unorderable nodes in functions using heapq

Dijkstra implementations in networkx.algorithms.centrality.betweenness
and networkx.algorithms.shortest_paths.weighted are affected. The Prim
implementation in networkx.algorithms.mst is also affected.

Although the A* implementation in astar.py already handles unorderable
nodes, it is also modified to avoid expensive hashing for tie breaking.
Merge pull request #1186 from ysitu/heapq

Handle unorderable nodes in functions using heapq