Fix handler hook documentation.

asio/src/doc/requirements/Handler.qbk

diff --git a/asio/src/doc/requirements/Handler.qbk b/asio/src/doc/requirements/Handler.qbk
index 92a3db6..5defcae 100644
--- a/asio/src/doc/requirements/Handler.qbk
+++ b/asio/src/doc/requirements/Handler.qbk
@@ -19,7 +19,7 @@
   [[expression] [return type] [assertion/note\npre/post-conditions]]
   [
     [``
-      using namespace asio;
+      using asio::asio_handler_allocate;
       asio_handler_allocate(s, &h);
     ``]
     [`void*`]
@@ -34,7 +34,7 @@
   ]
   [
     [``
-      using namespace asio;
+      using asio::asio_handler_deallocate;
       asio_handler_deallocate(p, s, &h);
     ``]
     []
@@ -48,7 +48,7 @@
   ]
   [
     [``
-      using namespace asio;
+      using asio::asio_handler_invoke;
       asio_handler_invoke(f, &h);
     ``]
     []

asio/src/doc/requirements/asynchronous_operations.qbk

diff --git a/asio/src/doc/requirements/asynchronous_operations.qbk b/asio/src/doc/requirements/asynchronous_operations.qbk
index 454c320..605615c 100644
--- a/asio/src/doc/requirements/asynchronous_operations.qbk
+++ b/asio/src/doc/requirements/asynchronous_operations.qbk
@@ -137,7 +137,7 @@
   void* asio_handler_allocate(size_t size,
                               bound_read_handler<ReadHandler>* this_handler)
   {
-    using namespace asio;
+    using asio::asio_handler_allocate;
     return asio_handler_allocate(size, &this_handler->handler_);
   }
 
@@ -145,7 +145,7 @@
   void asio_handler_deallocate(void* pointer, std::size_t size,
                                bound_read_handler<ReadHandler>* this_handler)
   {
-    using namespace asio;
+    using asio::asio_handler_deallocate;
     asio_handler_deallocate(pointer, size, &this_handler->handler_);
   }
 
@@ -153,7 +153,7 @@
   void asio_handler_invoke(const F& f,
                            bound_read_handler<ReadHandler>* this_handler)
   {
-    using namespace asio;
+    using asio::asio_handler_invoke;
     asio_handler_invoke(f, &this_handler->handler_);
   }