### Orientation of poset plot in Sage 6.3 vs 6.4

In older versions of Sage (6.3 and below), plotting a poset (or an acyclic graph with layout = "acyclic") gives a directed graph with arrows pointing up.

However, it seems like in Sage 6.4, the arrows now point down (and the bottom element appears at the top).

Is this a bug? Or are there any options I can tweak to reverse the orientation? I would expect the "correct" behaviour to be the one with the arrows pointing up; the Sage reference on layout_acyclic seems to agree.

(I noticed the discrepancy while running Sage 6.3 on the Sage Cell Server and Sage 6.4 on Sagemath Cloud)

Here's some code you can try:

```
Poset({0:[2],1:[2],2:[]}).show()
```