Javascript type conversion support

Add testcase for previous commit.
Add missing assert for future type conversions support that will use
the heap instead of pointer casts (for smart pointer type conversions).

Closes #1963

Lib/javascript/v8/javascriptruntime.swg

@@ -64,6 +64,7 @@
 #include <errno.h>
 #include <limits.h>
 #include <stdlib.h>
+#include <assert.h>
 %}
 
 %insert(runtime) "swigrun.swg";         /* SWIG API */