Added cos(DIRA) to two-track vertex variables
The MR adds the definition and the computation of the cosine of the DIRA, defined as the angle between the PV-SV direction and the vertex momentum.
The code has been compiled and run with both hlt1_pp_definition and hlt1_pp_validation. The variable has also been tested setting:
vertex.dira>0.999 vertex.dira>1.
/device/selections/lines/inclusive_hadron/src/TwoTrackMVALine.cu
In the first case the acceptance for MinBias events is reduced to 61/5000 events, from 82/5000. In the second case the acceptance goes to 0, so the variable should behave as expected.