fix save_if_interesting

The value of `classified`, `bits_new`, and `cksum`, were not always
correctly maintained.
 1. In the past, `afl->queue_top->exec_cksum` was always assigned when
    `add_to_queue`, however it became conditional since cd57641705.
    This doesn't change correctness because calibrate_case() will
    calculate the checksum. However, this mean one calibration run is
    wasted.

 2. Sometimes `classified` is set incorrectly.
    For example, this code snippet
    ```
    new_bits = has_new_bits_unclassified(afl, afl->virgin_bits);
    classified = 1;
    ```
    should be changed to
    ```
    new_bits = has_new_bits_unclassified(afl, afl->virgin_bits);
    if (new_bits) classified = 1;
    ```

This commit fixed above issues and use macros to make the code easier to
understand. This should prevent to forget to set classified in the
future (like the bug fixed by 30c93d1321).

The macros also defers the calculations to where the values are really
needed. This could save cpu if the code returns earlier. For example,
if a case is timeout first and not timeout the second time, the current
code does classify_counts, which is not always needed.

include/afl-fuzz.h

@@ -1216,7 +1216,6 @@ u8 *describe_op(afl_state_t *, u8, size_t);
 #endif
 u8 save_if_interesting(afl_state_t *, void *, u32, u8);
 u8 has_new_bits(afl_state_t *, u8 *);
-u8 has_new_bits_unclassified(afl_state_t *, u8 *);
 #ifndef AFL_SHOWMAP
 void classify_counts(afl_forkserver_t *);
 #endif