Fixed accumulating error in positioning (changed int to float division)

Dots indicating page positions were slightly offset in relation to slider "window", because horizontal distance between them was truncated to integers. The error for dot grew proportionally with further dot positions, as truncation error got multiplied by dot index. With more than ~10 pages it was clearly visible. 

Replacing int distance with floats increased accuracy and with this patch sliders with large pagecounts display ok.