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 to 50-60%.
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 performance (track efficiency vs track-jet dR) are shown in attachment (the blue vs red line)

![image](https://cloud.githubusercontent.com/assets/5022358/2970921/55932c26-db63-11e3-9e37-06577b26d4bd.png)