Änderungen

Handle null/code comparison
Previously `null` was always treated as of type handle in comparisons
but code is internally represented as integer so we had a mismatch. To
fix this we don't convert code to integer implicitly but we have to call
`code2int` explicitely. This makes sense since we can use code in 
typechecking but int in compiling.
 (commit: c50f361)