Add a wrapper to save a moeoMetric in an eoStat

Example:
    moeoHyperVolumeDifferenceMetric<OVT> * m_hypervolume = new moeoHyperVolumeDifferenceMetric<OVT>(true,1.1);
    moeoBinaryMetricStat<EOT>* hypervolume = new moeoBinaryMetricStat<EOT>( *m_hypervolume, "hyp-vol" );
    checkpoint.add( *hypervolume );

moeo/src/moeo

@@ -207,6 +207,7 @@
 #include <utils/moeoAverageObjVecStat.h>
 #include <utils/moeoBestObjVecStat.h>
 #include <utils/moeoBinaryMetricSavingUpdater.h>
+#include <utils/moeoBinaryMetricStat.h>
 #include <utils/moeoConvertPopToObjectiveVectors.h>
 #include <utils/moeoDominanceMatrix.h>
 #include <utils/moeoObjectiveVectorNormalizer.h>

moeo/src/utils/moeoBinaryMetricStat.h

@@ -0,0 +1,59 @@
+
+
+template <class MOEOT, class T = double>
+class moeoBinaryMetricStat : public eoStat<MOEOT, T>
+{
+public:
+    /** The objective vector type of a solution */
+    typedef typename MOEOT::ObjectiveVector ObjectiveVector;
+
+    moeoBinaryMetricStat(
+            moeoVectorVsVectorBinaryMetric<ObjectiveVector, T> & metric,
+            std::string description,
+            T default_value = 0
+        ) :
+            eoStat<MOEOT,T>( default_value, description),
+            _metric(metric),
+            _first_gen(true)
+    {}
+
+    virtual std::string className(void) const
+        { return "moeoBinaryMetricStat"; }
+
+
+    virtual void operator()( const eoPop<MOEOT> & pop )
+    {
+        if( pop.size() ) {
+            if( _first_gen ) {
+                _first_gen = false;
+            } else {
+              // creation of the two Pareto sets
+              std::vector < ObjectiveVector > from;
+              std::vector < ObjectiveVector > to;
+              for (unsigned int i=0; i<pop.size(); i++) {
+                from.push_back( pop[i].objectiveVector() );
+              }
+              for (unsigned int i=0 ; i<_prev_pop.size(); i++) {
+                to.push_back( _prev_pop[i].objectiveVector() );
+              }
+
+              // compute and save
+              this->value() = _metric(from,to);
+            } // if first gen
+
+            // copy the pop
+            _prev_pop = pop;
+        } // if pop size
+    }
+
+protected:
+    /** binary metric comparing two Pareto sets */
+    moeoVectorVsVectorBinaryMetric<ObjectiveVector, double> & _metric;
+
+    /** (n-1) population */
+    eoPop<MOEOT> _prev_pop;
+
+    /** is it the first generation ? */
+    bool _first_gen;
+
+};