Add context manager for reversing a graph.
Make `reversed` always do a noncopy.
Use nx.utils.reversed in kosaraju scc.
Cleanup code a bit more.
Fix hash randomization issue in unittest.
Missed one more.
Add smoke test when there is no mapping.
Merge pull request #1159 from chebee7i/hashranderror

Fix hash randomization error.
Merge pull request #1156 from chebee7i/reversed_cm

Add context manager for reversing a graph.
Correct reversed docstring and add reference in documentation