Fix mzscheme static variable wrappers

$argnum needs to be expanded in the 'varin' typemap which shares
code used by the 'in' typemap.
Setting the static variable is also a function call (argnum=1).

Added class examples - needs static variables to work
Test newly working test cases with this fix

Examples/mzscheme/class/example.i

@@ -0,0 +1,9 @@
+/* File : example.i */
+%module example
+
+%{
+#include "example.h"
+%}
+
+/* Let's just grab the original header file here */
+%include "example.h"