Prusa Mendel i2 modified z-axis endstop holder

It happend too often that the end stop for the z-axis was not in the right position resulting in a lot of unplanned work to get the machine up and running again. To prevent this, I added a second screw to the end stop and enlarged the arms so that they embrace the axle. This should prevent the end stop from being bent out of position. The endstop switch can be mounted with screws or a cable tie.