Fix memory leak in ME0SegmentMatcher

Fixes a small memory leak in ME0SegmentMatcher that looks to be proportional to the number of tracks.  At 140 pileup this is about half a Mb per event.
Plot of retained memory before an after below.

Leak pointed out by David Lange.

![me0segmentmatcher](https://cloud.githubusercontent.com/assets/6480160/4182520/bdc7b9ba-372f-11e4-9a30-49720ca44527.png)