Add alloc_construct_n overload for input iterators

doc/alloc_construct.qbk

@@ -67,6 +67,9 @@ void alloc_construct_n(A& a, T* p, std::size_t n);
 template<class A, class T>
 void alloc_construct_n(A& a, T* p, std::size_t n, const T* l, std::size_t m);
 
+template<class A, class T, class I>
+void alloc_construct_n(A& a, T* p, std::size_t n, I begin);
+
 } /* boost */
 ```
 
@@ -109,6 +112,16 @@ const T* l, std::size_t m);`]
 `std::allocator_traits<A>::construct(a, &p[i], l[i % m])`.]]
 [[Remarks]
 [If an exception is thrown destroys each already constructed `j`-th element in
+reverse order by calling `std::allocator_traits<A>::destroy(a, &p[j])`.]]]]]
+[[`template<class A, class T, class I> void alloc_construct_n(A& a, T* p,
+std::size_t n, I begin);`]
+[[variablelist
+[[Requires][`A` is an /Allocator/; `I` is an /InputIterator/]]
+[[Effects]
+[Constructs each `i`-th element in order by calling
+`std::allocator_traits<A>::construct(a, &p[i], *begin++])`.]]
+[[Remarks]
+[If an exception is thrown destroys each already constructed `j`-th element in
 reverse order by calling `std::allocator_traits<A>::destroy(a, &p[j])`.]]]]]]
 
 [endsect]