Jet core tracking step 

@cerati @rovere
This adds an iteration in tracking dedicated to reconstruct tracks in jet high pt core (DeltaR < ~ 0.1) where the efficiency typically drops below 60%.
The additional step only act in the core of caloJets with pt > 100.

This is the initial version and further tuning is expected in next releases, current improvements are shown in attachment

![image](https://cloud.githubusercontent.com/assets/5022358/2971351/49bf81c8-db69-11e3-99ee-bef56e0126e2.png)