Putting too many steps out of order results in an error that is not usually seen in Ruffus

[claresloggett]

We can use the usual Ruffus functionality where we put a step out of order and use the task name as a string, and this is ok:

@follows('first_task')
def second_task():
    ....

def first_task():
    ....

However if we put two tasks before the same dependency task, we get an error:

@follows('first_task')
def second_task():
    ....

@follows('first_task')
def other_second_task():
    ....

def first_task():
    ....

The second @follows('first_task') will throw an error like
ruffus.graph.error_duplicate_node_name: [pipeline.first_task] has already been added

This does not seem to happen when using straight ruffus scripts, without rubra.