Fix Pull dialog showing with Spanish translation

This fix https://github.com/gitextensions/gitextensions/issues/1509

![Captura](https://f.cloud.github.com/assets/3075551/45471/30d38040-5787-11e2-98d2-7df156c7b971.JPG)

Fixed:
![Captura_Fixed](https://f.cloud.github.com/assets/3075551/45485/aff06112-5788-11e2-8de1-2773c045c1b3.JPG)