Validator: explicitly include <algorithm>

src/validator.h

@@ -8,6 +8,7 @@
 
 #include <string>
 #include <set>
+#include <algorithm>
 
 #include <pv/pvIntrospect.h>
 
@@ -273,4 +274,4 @@ private:
 };
 }}
 
-#endif
+#endif