Hi,

I need to find a way to label all reachable nodes in a directed graph starting at a specific node. Is there a short way to do this?

Currently I use this:

```
graph = get_graph()
is_reachable = graph.new_vp("bool")
start_vertex = get_start_vertex()
tc = gt.transitive_closure(graph)
is_reachable[start_vertex] = True
for node in tc.vertex(start_vertex).out_neighbors():
is_reachable[graph.vertex(node)] = True
```

This works, but seems quite inefficient, since I don't need the full transitive closure (although I have multiple such start vertexes).

Another possibility should be a raw DFS but this needs far more LOC, since it needs to stop when it backtracks and therefore needs a custom visitor.

Gerion