DT meantimer tune

A small tuning of MT reco following the enabling of realistic hit uncertainties. A very small but consistent improvement in chi2, resolution, efficiency etc in RelVals.
![image](https://cloud.githubusercontent.com/assets/5595497/3083266/6b3e0eca-e4e0-11e3-8b13-0dec66aad3fb.png)
![image](https://cloud.githubusercontent.com/assets/5595497/3083271/86a599a8-e4e0-11e3-90f1-6ebb1c6d34aa.png)

Due to tightened chi2 cuts in segment building the numbers of hits become lower, this is expected (quality improves and efficiency does not suffer):
![image](https://cloud.githubusercontent.com/assets/5595497/3083260/4622c22a-e4e0-11e3-8c3b-a21e9329f22d.png)