Fix "protocol error" in usage of MethodVisitor

If nothing else, make sure to grab this commit: https://github.com/krestenkrab/kilim/commit/b25d17c95d8017ac8f4854dac507081fd4e1b4f1, which is a "protocol error" in using MethodVisitor: we need to call MethodVisitor#visitEnd() even for abstract methods.

Other than that, this fixes some wrong usage of the Detector API (I don't know if anyone else is using it).