Remove ugly global variables
Remove ugly global variables

You don't have to set persistant objects (like lists) as global or even nonlocal thanks to closure.
But, to modify the int dfs_time in the context of the tarjan_recursif, you just have to make it nonlocal. Python is going to look in every parent namespace to find such a variable.

To quote Guido :

> Namespaces are one honking great idea -- let's do more of those!
jilljenn/tryalgo