Fix for vanishing thumbnails, when browser-zoom is active.
Due to a bug in jquery, outerwidth() returns the floor of the
actual outerwidth, if the browser is zoom to a value other than
100%. height() returns the floating point value.
This caused galleria to compute a wrong width for the 'thumbnails'
element. The container was not wide enough and the last thumbnail was
displayed in the next line, thus was effectively invisible.