Reduced the maximum track-cluster distance permissable for a matched clu...

...ster.

Old value was 0.5 mm, new value is 0.1 mm.
This is motivated by the histogram of track-cluster distance.

![cluster-track_dist](https://cloud.githubusercontent.com/assets/8256377/3830698/9a6993ba-1d8c-11e4-8b8d-5764e13134cc.png)

Also added a check that the requested number of events is not greater than the total
and allow the user to input -1 from the command line to mean "all events".