Don't use _T() in public headers used under Unix.

Avoid conflict with the Sun CC standard headers (see #10660).

Also update the change log to mention _T() changes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@61872 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/cshelp.h

@@ -134,7 +134,7 @@ public:
                                  const wxPoint& pt,
                                  wxHelpEvent::Origin origin)
     {
-        wxCHECK_MSG( window, false, _T("window must not be NULL") );
+        wxCHECK_MSG( window, false, wxT("window must not be NULL") );
 
         m_helptextAtPoint = pt;
         m_helptextOrigin = origin;