Define and use IteratorRange

src/MemoryX.h

@@ -727,4 +727,16 @@ Final_action<F> finally (F f)
    return Final_action<F>(f);
 }
 
+/*
+ * A convenience for use with range-for
+ */
+template <typename Iterator>
+struct IteratorRange : public std::pair<Iterator, Iterator> {
+   IteratorRange (Iterator &&a, Iterator &&b)
+      : std::pair<Iterator, Iterator> { std::move(a), std::move(b) } {}
+
+   Iterator begin() const { return this->first; }
+   Iterator end() const { return this->second; }
+};
+
 #endif // __AUDACITY_MEMORY_X_H__