CStringParam does not use `default_value'

In typehandlers.inttype.IntParam, the convert_python_to_c() method uses the `default_value' attribute to decide if a default value will be passed to the var that will read an argument and to set the correct `optional' flag in parse_params.add_parameter().

Is there any chance to make CSringParam do the same? I've changed it in my working copy and nothing seemed to stop to work. I have to run all the tests before making sure it will not break anything and then I'll format a patch with that change if it helps.

Thank you!