[glibmm] Glib::RefPtr: add "release()" method

[Marcin Kolny <mkolny src gnome org>]

commit 07ba42710cc2f7d15c070c44a4d1c1c64d66de61
Author: Marcin Kolny <marcin kolny gmail com>
Date:   Fri Jul 24 09:26:47 2015 +0200

    Glib::RefPtr: add "release()" method
    
    https://bugzilla.gnome.org/show_bug.cgi?id=752812
    
        * glib/glibmm/refptr.h: "release" method gives an access to managed
          underlying object, releasing RefPtr's ownership. Method is useful
          e.g. in wrappers of functions containing transfer-full arguments.

 glib/glibmm/refptr.h |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)
---
diff --git a/glib/glibmm/refptr.h b/glib/glibmm/refptr.h
index 1aca555..4a23d96 100644
--- a/glib/glibmm/refptr.h
+++ b/glib/glibmm/refptr.h
@@ -132,6 +132,13 @@ public:
    */
   inline void reset();
 
+  /** Release the ownership of underlying instance.
+   *
+   * RefPtr's underlying instance is set to nullptr, therefore underlying object can't be accessed through 
this RefPtr anymore.
+   * @return an underlying instance.
+   */
+  inline T_CppObject* release() __attribute__((warn_unused_result));
+
   /** Dynamic cast to derived class.
    *
    * The RefPtr can't be cast with the usual notation so instead you can use
@@ -355,6 +362,14 @@ void RefPtr<T_CppObject>::reset()
   this->swap(temp);
 }
 
+template <class T_CppObject> inline
+T_CppObject* RefPtr<T_CppObject>::release()
+{
+  T_CppObject *tmp = pCppObject_;
+  pCppObject_ = nullptr;
+  return tmp;
+}
+
 template <class T_CppObject>
   template <class T_CastFrom>
 inline