fix warning text and margin. fixes #8715

Before:

![owncloud604_en](https://cloud.githubusercontent.com/assets/231068/3077749/e4f1a65a-e440-11e3-883e-ccc3a6ee3642.png)

After patch:

![owncloud_uygulamayonetici1](https://cloud.githubusercontent.com/assets/231068/3086437/e169c49c-e533-11e3-9455-461bd331f7d9.png)

- also fixes the margin issue in username field.

@jancborchardt