spline parametrization types added


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1949 29e17f8d-cf37-471e-a288-72cc03a76eda
endpoint conditions moved to QwtSplineC1


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1950 29e17f8d-cf37-471e-a288-72cc03a76eda