Fix vertical alignment of input-append button in nav-bar

Fixes the vertical alignment of input-append buttons in nav-bar. Example of the wrong alignment here: http://jsfiddle.net/jendrik/LXLBJ/1/

This is a revert of the fix for bug #4680, which was an improper fix for the problem, now causing this bug. (The problem was properly fixed #4540 as far as I see).