Fix compiler errors and warnings for clang 6 and C++11

ReferencePosition.h and .cc: static init of float not supported in older C++
    so move that to a .cc file for maximum compatibility
tests/csv.cc varargs not supported with references
Csv.cc LSST_SPECIALIZE_GET needed to set errno=0 to avoid spurious errors
  (thanks to K-T for the suggested fix)
csvUtils.h had a typo in its include-once guard that clang 6 caught