Fix behaviour of LauBlattWeisskopf::Covariant option for parent Blatt-Weisskopf factor - the correct expressions were not being calculated for spins greater than 1. Also make use of setSpinType in NR models that want pure Legendre polynomial spin factors, where before we were kludging with ignoreMomenta. Fix TestCovariant, which was broken since [403] due to this ignoreMomenta kludge, by allowing user to override the enforced pure-Legendre spin factors in LauBelleNR.

git-svn-id: svn+ssh://phab.hepforge.org/source/laurasvn/trunk@419 30227d83-a2f9-49e9-9e98-657c83b2c86a