Allow operator() in AnalyticalCoordFunction
Classes that implemented closed-form ('analytical') coordinate functions for GeometryGrid currently need to derive from the AnalyticalCoordFunction class, and implement the method
void evaluate ( const DomainVector &x, RangeVector &y ) const
This appears a bit old-fashioned.
This patch allows to alternatively implement
RangeVector operator() ( const DomainVector& x) const
If that method exists, GeometryGrid will use it. Otherwise, it will fall back on 'evaluate'. Therefore, while this patch is an interface enhancement, it does not break any existing code.