This function computes the least integer value not less than val.

Examples:

 IloCeil(IloInfinity) is IloInfinity.
 IloCeil(-IloInfinity) is -IloInfinity.
 IloCeil(0) is 0.
 IloCeil(0.4) is 1.
 IloCeil(-0.4) is 0.
 IloCeil(0.5) is 1.
 IloCeil(-0.5) is 0.
 IloCeil(0.6) is 1.
 IloCeil(-0.6) is 0.