[igraph] Neighbors Function

[Tao Wang]

Hi,

According to online document, predecessors function is equivalent to calling 
the Graph.neighbors method with type=IN, and successors is equivalent to 
calling the Graph.neighbors method with type=OUT.
However, in my test, they are not totally equivalent. The returned list from 
Graph.neighbors always includes the input vertex, while those from predecessors 
and successors don’t. So the size of returned list from neighbors is always 
larger 1 than those from other two methods.
Not sure whether it is a bug?

Best,
Tao