COMP: Add testing for tube::SplineND::ExtremeConjGrad.

The line number moved, so a CppCheck "unmatchedSuppression" error occurred and
a new "unusedFunction" error occurred.

Remove the suppression and add testing code.

Change-Id: I4f026a820dbf61db8595baa1042231fb18b29287
Merge pull request #73 from thewtex/CppcheckError

COMP: Add testing for tube::SplineND::ExtremeConjGrad.