Improve RunScript() error message when using old WebKit

Don't put WebKit in all capitals and, more importantly, make it clear
that this is related to running JavaScript to the user.

src/gtk/webview_webkit.cpp

@@ -953,7 +953,7 @@ bool wxWebViewWebKit::RunScript(const wxString& javascript, wxString* output)
 {
     if ( output != NULL )
     {
-        wxLogWarning(_("Returning output is not supported on WEBKIT1"));
+        wxLogWarning(_("Retrieving JavaScript script output is not supported with WebKit v1"));
         return false;
     }