ARC: Evicted entries from T1 are not tracked in the ghost list

[erwanor]

gc := gcache2.New(10).ARC().Build()

for i := 0; i <= 10; i++ {
    value := fmt.Sprintf("val%d", i)
    gc.Set(i, value)
}

Upon inspection of the cache internal state, it appears that:

• As expected, all the key/values are stored in the tier 1 cache t1
• The key 0 with value val0 is correctly evicted from t1

However, the ghost list b1 does not keep track of the evicted key 0.

See: ARC: A Self-Tuning, Low Overhead Replacement Cache - https://www.usenix.org/legacy/events/fast03/tech/full_papers/megiddo/megiddo.pdf

[erwanor]

The issue will be considered fixed when a unit-test addressing it hits master.