Describe conversion to directed graph
Some pagerank implementations work with multigraphs

Remove restrictions on multigraphs in pagerank_numpy() and pagerank_scipy().
Clarify in comments.
pagerank() degree should consider weights
Clarify input type. Remove multigraph guard.
Warn on zero out-degree (row-sum)
Match convergence tolerances

Match convergence criteria to be the same for pagerank and pagerank_scipy
Normalize negative entries to match pagerank algs

Now pagerank_scipy() is the same as pagerank().
That is, both will possibly produce the same incorrect answer if you put in negative weights.
Merge pull request #1001 from hagberg/stochastic-zero

Stochastic zero row + pagerank

The various pagerank(), pagerank_numpy(), and pagerank_scipy() should produce the same results now for cases with weighted graphs with zero row sums or negative weights.   The negative weight case may produce answers but I don't know if they are meaningful (certainly that breaks the intentions and assumptions of the algorithm.)  The convergence tolerances now match between implementations too.