qNN headers: only promise what we can keep

In general, we can't make the qNN types behave exactly like their
C++NN std counter-parts, because their exact semantics and
implementation may depend on C++NN language features, while qNN are
back-ports to C++ standards older than NN.

Adjust the warning message accordingly.

Thanks to Eddy for noticing.

Change-Id: I8533214549f2140a99e2216e3bcd979263fe100c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
(cherry picked from commit f1c41382af0fd3e769b5792891b204ebeecd3bd2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/global/q20algorithm.h

@@ -12,9 +12,9 @@
 //  W A R N I N G
 //  -------------
 //
-// This file is not part of the Qt API. Types and functions defined
-// in this file will behave exactly as their std counterparts. You
-// may use these definitions in your own code, but be aware that we
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
 // will remove them once Qt depends on the C++ version that supports
 // them in namespace std. There will be NO deprecation warning, the
 // definitions will JUST go away.

src/corelib/global/q20functional.h

@@ -11,9 +11,9 @@
 //  W A R N I N G
 //  -------------
 //
-// This file is not part of the Qt API. Types and functions defined
-// in this file will behave exactly as their std counterparts. You
-// may use these definitions in your own code, but be aware that we
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
 // will remove them once Qt depends on the C++ version that supports
 // them in namespace std. There will be NO deprecation warning, the
 // definitions will JUST go away.

src/corelib/global/q20iterator.h

@@ -11,9 +11,9 @@
 //  W A R N I N G
 //  -------------
 //
-// This file is not part of the Qt API. Types and functions defined
-// in this file will behave exactly as their std counterparts. You
-// may use these definitions in your own code, but be aware that we
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
 // will remove them once Qt depends on the C++ version that supports
 // them in namespace std. There will be NO deprecation warning, the
 // definitions will JUST go away.

src/corelib/global/q23functional.h

@@ -10,9 +10,9 @@
 //  W A R N I N G
 //  -------------
 //
-// This file is not part of the Qt API. Types and functions defined
-// in this file will behave exactly as their std counterparts. You
-// may use these definitions in your own code, but be aware that we
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
 // will remove them once Qt depends on the C++ version that supports
 // them in namespace std. There will be NO deprecation warning, the
 // definitions will JUST go away.

src/corelib/global/qxpfunctional.h

@@ -9,9 +9,9 @@
 //  W A R N I N G
 //  -------------
 //
-// This file is not part of the Qt API. Types and functions defined
-// in this file will behave exactly as their std counterparts. You
-// may use these definitions in your own code, but be aware that we
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
 // will remove them once Qt depends on the C++ version that supports
 // them in namespace std. There will be NO deprecation warning, the
 // definitions will JUST go away.