Directed Gnp model (fast version) has wrong start index

For the directed graph version of the Gnp model the starting target has to be at v=0 not v=1 or no out-edges will ever be generated from node 0.
Fix failing test in planted_partition_graph

Update size to 218
Selfloops counted twice

Fix bug where Graph selfloops get counted twice when converting to scipy sparse matrix.
Add highest-label preflow-push algorithm for maximum flow
Fix python3 compat in preflow-push maxflow algorithm
Fix typo and avoid line breaking after hyphen in preflow-push maxflow algorithm
Fix indent level in preflow-push maxflow algorithm
Fix python2.6 compat in preflow-push maxflow algorithm
Fix python2.6 compat in preflow-push maxflow algorithm (cont'd)
Fix python2.6 compat in preflow-push maxflow algorithm (cont'd)
Add testcases to test_maxflow_large_graph

These networks are generated using the same generators and parameters as
in the 1st DIMACS Implementation Challenge. But they are not the same as
the actual DIMACS instances due to different random numbers being used.
Clean up heuristics logic in preflow-push maxflow algorithm

This ensures that during phase 1, if a node is found to be disconnected
from the sink in the residual network, it will not be further processed
until phase 2.
Minor readability changes in preflow-push maxflow algorithm
Allow retrieving residual network in preflow-push maxflow algorithm

The interface is intended to be internal and for use in the minimum cut
algorithm.
Fix examples in docstrings of preflow-push maxflow algorithm
Make frequency mean frequency for preflow-push global relabeling
Include bz2 archives in manifest
Fix examples in docstrings of preflow-push maxflow algorithm (cont'd)
Include .bz2 files in networkx.algorithm.flow
Fix max_height calculation in global_relabel in preflow-push maxflow