When navigation tabs use more space than their container (e.g. /settings), tab buttons are displayed in order to horizontally scroll to non visible tabs.

The javascript function (in application.js) displayTabButtons takes care of settting these tab buttons to a visible / non-visible state. This function is theoretically supposed to work for severeal tab navigations. It applies it's logic to all divs, with class .tabs in a for each loop.

To my knowledge redmine does not have pages with several of these tab navigations. If a plugins tries to use this funtionality, though, it will run into the following problem: If one tab navigation meets the condition to be displayed, all other tab navigations on the page (even when not needed) will have the tab buttons for horizontal scrolling enabled.

This patch fixes this false behaviour.