[3011582] stix_fonts_demo.py assert error

When matplotlib is compiled without -DNDEBUG, we get this error on one of the example:

$ python stix_fonts_demo.py
python2.6: CXX/cxx_extensions.cxx:1320: virtual Py::PythonExtensionBase::~PythonExtensionBase(): Assertion `ob_refcnt == 0' failed.
Aborted

svn path=/trunk/matplotlib/; revision=8405

src/ft2font.cpp

@@ -686,25 +686,28 @@ FT2Font::FT2Font(std::string facefile) :
 
   int error = FT_New_Face( _ft2Library, facefile.c_str(), 0, &face );
 
-
   if (error == FT_Err_Unknown_File_Format ) {
     std::ostringstream s;
     s << "Could not load facefile " << facefile << "; Unknown_File_Format" << std::endl;
+    ob_refcnt--;
     throw Py::RuntimeError(s.str());
   }
   else if (error == FT_Err_Cannot_Open_Resource) {
     std::ostringstream s;
     s << "Could not open facefile " << facefile << "; Cannot_Open_Resource" << std::endl;
+    ob_refcnt--;
     throw Py::RuntimeError(s.str());
   }
   else if (error == FT_Err_Invalid_File_Format) {
     std::ostringstream s;
     s << "Could not open facefile " << facefile << "; Invalid_File_Format" << std::endl;
+    ob_refcnt--;
     throw Py::RuntimeError(s.str());
   }
   else if (error) {
     std::ostringstream s;
     s << "Could not open facefile " << facefile << "; freetype error code " << error<< std::endl;
+    ob_refcnt--;
     throw Py::RuntimeError(s.str());
   }
 
@@ -720,6 +723,7 @@ FT2Font::FT2Font(std::string facefile) :
   if (error) {
     std::ostringstream s;
     s << "Could not set the fontsize for facefile  " << facefile << std::endl;
+    ob_refcnt--;
     throw Py::RuntimeError(s.str());
   }
 
@@ -739,7 +743,6 @@ FT2Font::FT2Font(std::string facefile) :
    if ( style_name == NULL )
      style_name = "UNAVAILABLE";
 
-
   setattr("postscript_name", Py::String(ps_name));
   setattr("num_faces",       Py::Int(face->num_faces));
   setattr("family_name",     Py::String(family_name));