added wxS(); use it in a couple of places

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@50987 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/wxchar.h

@@ -251,6 +251,9 @@
 /* and _() in wxWidgets sources */
 #define wxT(x)       _T(x)
 
+/* this macro exists only for forward compatibility with wx 3.0 */
+#define wxS(x)       _T(x)
+
 /* a helper macro allowing to make another macro Unicode-friendly, see below */
 #define wxAPPLY_T(x) _T(x)