Helix

Speed ups and cleanup in Helix computation
In particular the iteration code in for ArbitraryPlaneCrossing has been "linearized"
The maximum number of iterations reduced to 20 (for good solution never seen exceeding 7)
log info degraded to log debug

15% speedup of Analytical propagator 

Regression:
As usual, when touching arithmetic code regression are observed.
Conversions are, as usual, affected more than others...
Fully consistent with what already observed when changes occur in optimization by the compiler