region: add union-assignment operator

cruft/util/region.hpp

@@ -258,6 +258,15 @@ namespace cruft {
     }
 
 
+    //-------------------------------------------------------------------------
+    template <typename T, size_t S>
+    region<S,T>&
+    operator|= (region<S,T> &a, region<S,T> const &b)
+    {
+        return a = a | b;
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     /// Construct a region that consists of the overlapping portions of two
     /// supplied regions.