Added rounding to the percent of page in status bar.

If the user scrolled to 1% of the page there was 0% shown and with 50G vimb
browser showed 49% in status bar. This patch adapts the rounding of the values
in the status bar so that they fit to the done scrolling.
Fixed scrolling over the end of the page.

If the scrolling reached the end of the page, further scrolling set higher
adjustments. If the user scrolled to top, this didn't take effect immediately.