Untested SOS tracking code.

  THcDriftChamber
    New flag fHMSStyleChambers to determine if HMS or SOS style
    tracking should be done.  Flag is set on if the spectrometer
    name begins with 'h'.
    THcDriftChamber::LeftRight fSmallAngleApprox must be set and
    fHMSStyleChambers must be off to do SOS style.
    If not HMS style, ignore all the Yplane optimizations
  THcDC
    SOS code does "project to chamber" in link stubs.  Need to evaluate
    if this is necessary, or if HMS style should also do it.