libpbd: add operator<< for PropertyChange

libs/pbd/pbd/property_basics.h

@@ -173,4 +173,8 @@ private:
 
 }
 
+namespace std {
+ostream& operator<< (std::ostream& os, PBD::PropertyChange const & pc);
+}
+
 #endif /* __libpbd_property_basics_h__ */

libs/pbd/property_list.cc

@@ -89,3 +89,9 @@ OwnedPropertyList::add (PropertyBase& p)
 }
 
 
+std::ostream&
+std::operator<< (std::ostream& os, PropertyChange const & pc)
+{
+	pc.dump (os);
+	return os;
+}