Allow augmenting the return value in unsafe mode

[jbachorik]

Sometimes it might be useful to augment the return value captured in location=@Location(Kind.RETURN) or location=@Location(Kind.CALL) handlers.

Eg. the following piece of code would put a cap on the value that could be returned by the intercepted method.

@BTrace(unsafe = true)
public class ArgsReturnAugmented {
    @OnMethod(clazz="TestClass", method="testMethod", location=@Location(value=Kind.RETURN))
    public static long args(@Self Object self, @Return long ret, String a, long b, String[] c, int[] d) {
        println("args");
        return ret > 100 ? 100 : ret;
    }
}

Since this functionality can bring instability to the traced application it is limited to the unsafe mode only.