using BoundaryCondition in QwtSplineLocal


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1952 29e17f8d-cf37-471e-a288-72cc03a76eda
boundary calculations isolated


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1953 29e17f8d-cf37-471e-a288-72cc03a76eda