gui.ios: wrong z-index for native client warning

That warning that appears at your first login with a smartphone doesn't have the highest z-index so some interface elemnts appear over it and the result is a little ugly and sometimes is impossible to choose an option from that popup:

![screenshot_2014-12-10-18-57-35](https://cloud.githubusercontent.com/assets/3270352/5391113/c430e0ac-8116-11e4-985d-d1afce4fcd87.png)

This happens because this popup uses "browser" id, which is the same id as the left panel. May this be the first error? I think that ids are supposed to be unique.
Anyway, this makes both panels to have the same z-index: 10000, which makes the last one to appear to be over the previous one.
Making the native-client popup to have a higher z-index will fix this issue.

Issue tested with Android and iPhone.