BUG: EruoPP limits fix

Closes #436
![figure_1](https://cloud.githubusercontent.com/assets/2071643/3299851/10e77dfe-f619-11e3-9bf6-d4d27a9325a4.png)

You're not going to like it!  I chose the nearest values to 1 decimal place corresponding to plots describing the EuroPP internally (MetOffice).  i.e. chose them visually.
I could define a rectangle in lat-lon, transform it to this projection to determine more accurate limits if you would like?