mit-crpg/openmc — pull request #350 by nhorelik (2014-12-31 17:54:21+00:00)
Title: Flipped y pixels for meshline plotting

As pointed out on users group, there was an issue with meshlines plotting. Specifically, the y pixels on the plot were flipped.

The xml files in tests/test_filter_mesh_3d/ can be used to test this, with the following plots.xml

```xml

0. 0. 0.
500 500
2000 2000

```
tally.xml

```xml

rectangular
0 0 -183.00
182.07 90 183.00
17 17 17

total

```

and the following change in the lattice at the bottom of geometry.xml

```xml

rectangular
21 21
-224.91 -224.91
21.42 21.42

7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7
7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7
7 7 7 7 7 7 7 8 8 8 8 8 8 8 7 7 7 7 7 7 7
7 7 7 7 7 8 8 8 8 8 8 8 8 8 8 8 7 7 7 7 7
7 7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 7 7
7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 7
7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 7
7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7
7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7
7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7
7 7 8 8 8 8 7 7 7 8 8 8 8 8 8 8 8 8 8 7 7
7 7 8 8 8 8 7 7 8 8 8 8 8 8 8 8 8 8 8 7 7
7 7 8 8 8 8 7 8 8 8 8 8 8 8 8 8 8 8 8 7 7
7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7
7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 7
7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 7
7 7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 7 7 7 7
7 7 7 7 7 8 8 8 8 8 8 8 8 8 8 8 7 7 7 7 7
7 7 7 7 7 7 7 8 8 8 8 8 8 8 7 7 7 7 7 7 7
7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7
7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7

```

Should produce this output:

![1_plot](https://cloud.githubusercontent.com/assets/1110672/5589387/8e9e3310-90eb-11e4-870a-8a47a044f231.png)