Add an option to keep cubic spline  monotone, if the input is monotone.


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6765 04224531-1f84-46d8-96ce-875b9e37dce3
Add specification "Cubic Monotone" to sif-file table input.


git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6766 04224531-1f84-46d8-96ce-875b9e37dce3
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git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6767 04224531-1f84-46d8-96ce-875b9e37dce3