Log message:
update to gerbv 0.0.8

Graphical quirks fixed are:
- zooming around the mouse pointer.
- zooming several steps at once goes much faster. No calculation and
  redrawing in each zoom step, but in the last step.

When you click with the left mouse button on a layer button you
get a popup menu with color selection, load file and unload file.
That is on a "per layer-basis". The "global" "Open \ 
File..." menu is
removed in favor for this.