Extracted private GetTimeZone() to public wxGetTimeZone() function.

Created new wx/time.h header for this function, more time-related functions
will be added to it later.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69836 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/time.h

@@ -0,0 +1,21 @@
+/////////////////////////////////////////////////////////////////////////////
+// Name:        wx/time.h
+// Purpose:     Time-related functions.
+// Author:      Vadim Zeitlin
+// Created:     2011-11-27
+// RCS-ID:      $Id$
+// Copyright:   (c) 2011 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+/////////////////////////////////////////////////////////////////////////////
+
+/** @addtogroup group_funcmacro_time */
+//@{
+
+/**
+    Returns the difference between UTC and local time in seconds.
+
+    @header{wx/time.h}
+ */
+int wxGetTimeZone();
+
+//@}