Random dag generator

[abureyanahmed]

There is a bug in the random_dag function of

https://ipython.org/ipython-doc/3/parallel/dag_dependencies.html

The solution is to add the following line:

if G.has_edge(a, b):continue

before:

G.add_edge(a,b)

[Carreau]

This is suuuuper old documentation; this is not part of IPython anymore. I'll see if I can move that to ipyparallel.