Added DetachOldLog to avoid destruction of old log target

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@46579 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/log.tex

@@ -434,6 +434,13 @@ target but the log messages are also passed to the previous log target if any.
 
 Destroys the previous log target.
 
+\membersection{wxLogChain::DetachOldLog}\label{wxlogchaindetacholdlog}
+
+\func{void}{DetachOldLog}{\void}
+
+Detaches the old log target so it won't be destroyed when the wxLogChain object
+is destroyed.
+
 \membersection{wxLogChain::GetOldLog}\label{wxlogchaingetoldlog}
 
 \constfunc{wxLog *}{GetOldLog}{\void}

include/wx/log.h

@@ -415,6 +415,11 @@ public:
     // override base class version to flush the old logger as well
     virtual void Flush();
 
+    // call to avoid destroying the old log target
+#if wxABI_VERSION >= 20805 /* 2.8.5+ only */
+	void DetachOldLog() { m_logOld = NULL; }
+#endif
+
 protected:
     // pass the chain to the old logger if needed
     virtual void DoLog(wxLogLevel level, const wxChar *szString, time_t t);