title: Python-IGraph: Find neighbors of a node, only if connecting edges have certain attributes
body: <p>is there such a function premade in python-igraph (or also networkx, so I could adapt it to work in igraph), or do i have to implement it? </p>
  
  <p>If it doesnt exist yet, I would outlay it like that: </p>
  
  <ol>
  <li>Get the incident edges of the source node,</li>
  <li>only keep edges that meet the attribute criteria (for example, only edges with attribute "major")</li>
  <li>For the edges from 2., find the target nodes using the target property of the edge as  described <a href="http://igraph.org/python/doc/igraph.Edge-class.html" rel="nofollow">here</a></li>
  </ol>
  
  <p>Any improvements welcome!</p>