Add Javascript (JSC) support for type conversion

Fix types_directive testcase to ensure the %types code is actually
called and not just cast from one type to the other.

Lib/javascript/jsc/javascriptruntime.swg

@@ -11,6 +11,7 @@
 #include <string.h>
 #include <errno.h>
 #include <limits.h>
+#include <assert.h>
 %}
 
 %insert(runtime) "swigrun.swg";         /* SWIG API */