set NoToggleToOff flag when exporting Radio Button to PDF

Description of that flag can be found in
http://www.adobe.com/devnet/acrobat/pdfs/PDF32000_2008.pdf in Table 226
on p. 447.

diff -r c7da5153821f -r 402e450b79ef vcl/source/gdi/pdfwriter_impl.cxx
--- a/vcl/source/gdi/pdfwriter_impl.cxx	Tue Mar 02 17:07:25 2010 +0100
+++ b/vcl/source/gdi/pdfwriter_impl.cxx	Sun Mar 07 10:45:05 2010 +0100
@@ -11526,7 +11526,7 @@
         m_aWidgets.back().m_nPage		= m_nCurrentPage;
         m_aWidgets.back().m_eType		= PDFWriter::RadioButton;
         m_aWidgets.back().m_nRadioGroup = rBtn.RadioGroup;
-        m_aWidgets.back().m_nFlags |= 0x00008000;
+        m_aWidgets.back().m_nFlags |= 0x0000C000;   // NoToggleToOff and Radio bits
 
         // create radio button field name
         const rtl::OUString& rName = (m_aContext.Version > PDFWriter::PDF_1_2) ?