[glibmm] Threads::Private: Suggest use of thread_local.

[Murray Cumming <murrayc src gnome org>]

commit 7cb4a6c9409c1c2f9972e6439951e401043628d0
Author: Murray Cumming <murrayc murrayc com>
Date:   Sat Nov 28 12:59:28 2015 +0100

    Threads::Private: Suggest use of thread_local.

 glib/src/threads.hg |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/glib/src/threads.hg b/glib/src/threads.hg
index 3fa16f7..2cbd3f7 100644
--- a/glib/src/threads.hg
+++ b/glib/src/threads.hg
@@ -574,6 +574,8 @@ private:
  * It is recommended that all instances of this class are statically allocated.
  * The first time an instance is used (get(), set() or replace() is called)
  * glib allocates a scarce OS resource that cannot be deallocated.
+ *
+ * @deprecated Please use the thread_local keyword instead.
  */
 template <class T>
 class Private