added check for GTK 1.2

added symbol __WXGTK12__  (do not use GTK_MINOR_VERSION in your code
    as this is undefined anywhere outside wxGTK itself)
  updated wxGTK.spec for local builds
  fixed clipboard clear/setdata race
  test for wxConvLocal in dialogs sample


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@2291 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/symbols.txt

@@ -7,6 +7,7 @@ __X__           any X, but not GTK
 __WXMOTIF__     Motif
 __WXXT__        Xt; mutually exclusive with WX_MOTIF (?)
 __WXGTK__       GTK
+__WXGTK12__     GTK 1.2 or higher
 __WXMSW__       Any Windows
 __WXMAC__       MacOS
 __UNIX__        any Unix