Added MapNode helper methods HasNumericEntry and HasNumericVectorEntry.
Thus, an option may now be checked:
         doubleVector pt1, pt2;
         if (queryParams.HasNumericVectorEntry("start_point"))
         {
             queryParams.GetEntry("start_point")->ToDoubleVector(pt1);
         }
         else
         {
             Error(tr("Lineout requires start_point argument."));
             return;
         }
Added new QueryArugment exception where required size of a vector argument can be specified.

Resolves #1297


git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@20003 18c085ea-50e0-402c-830e-de6fd14e8384