Akima spline first implementation


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1861 29e17f8d-cf37-471e-a288-72cc03a76eda
akima spline implementation in one loop


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1862 29e17f8d-cf37-471e-a288-72cc03a76eda
testing different spline interpolations


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1863 29e17f8d-cf37-471e-a288-72cc03a76eda
curveeditor -> splineeditor


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1864 29e17f8d-cf37-471e-a288-72cc03a76eda