cubic spline with parabolic/cubic runout conditions


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1912 29e17f8d-cf37-471e-a288-72cc03a76eda
splinetest added


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1913 29e17f8d-cf37-471e-a288-72cc03a76eda