Log a warning on duplicate SID.
Currently when suricata-update encounters a rules with duplicate SIDs, it will silently use the one with the higher revision. While I believe this behaviour is correct, we should still log a warning.
On duplicate SID we should probably log the following as warnings:
- If revisions differ: Found duplicate rule ID %d, keeping one with higher revision.
- If revisions are equals: Found duplicate rule ID %s, keeping existing rule.