Fixed C# and CLI backends to check for null values when marshaling classes.
Fixed a bug by removing this weird looking code from the C# marshaller.

The test suite still passes too.
Re-generated the parser bindings with the latest fixes.
Fixed the AST converter code to deal with null values correctly.
Added support for default values of parameters.
Signed-off-by: Dimitar Dobrev <dpldobrev@yahoo.com>