FEAT: Filter duplicate messages

[carlwilson]

• Message classes made hash/equals safe, for use in HashSet;
• RepInfo now uses a HashSet to store messages and returns a derived list;
• removed line left in target script by mistake; and
• added comments to target script.

[codecov[bot]]

Codecov Report

Patch coverage: 93.33% and project coverage change: +0.16 :tada:

Comparison is base (dc26346) 46.87% compared to head (8d46131) 47.04%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## integration #839 +/- ## ================================================= + Coverage 46.87% 47.04% +0.16% - Complexity 1083 1097 +14 ================================================= Files 57 57 Lines 9050 9079 +29 Branches 1607 1622 +15 ================================================= + Hits 4242 4271 +29 Misses 4274 4274 Partials 534 534 ``` | [Impacted Files](https://codecov.io/gh/openpreserve/jhove/pull/839?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openpreserve) | Coverage Δ | | |---|---|---| | [...c/main/java/edu/harvard/hul/ois/jhove/RepInfo.java](https://codecov.io/gh/openpreserve/jhove/pull/839?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openpreserve#diff-amhvdmUtY29yZS9zcmMvbWFpbi9qYXZhL2VkdS9oYXJ2YXJkL2h1bC9vaXMvamhvdmUvUmVwSW5mby5qYXZh) | `55.63% <66.66%> (+1.02%)` | :arrow_up: | | [...c/main/java/edu/harvard/hul/ois/jhove/Message.java](https://codecov.io/gh/openpreserve/jhove/pull/839?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openpreserve#diff-amhvdmUtY29yZS9zcmMvbWFpbi9qYXZhL2VkdS9oYXJ2YXJkL2h1bC9vaXMvamhvdmUvTWVzc2FnZS5qYXZh) | `97.77% <97.67%> (+3.66%)` | :arrow_up: | | [...n/java/edu/harvard/hul/ois/jhove/ErrorMessage.java](https://codecov.io/gh/openpreserve/jhove/pull/839?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openpreserve#diff-amhvdmUtY29yZS9zcmMvbWFpbi9qYXZhL2VkdS9oYXJ2YXJkL2h1bC9vaXMvamhvdmUvRXJyb3JNZXNzYWdlLmphdmE=) | `100.00% <100.00%> (ø)` | | | [...in/java/edu/harvard/hul/ois/jhove/InfoMessage.java](https://codecov.io/gh/openpreserve/jhove/pull/839?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openpreserve#diff-amhvdmUtY29yZS9zcmMvbWFpbi9qYXZhL2VkdS9oYXJ2YXJkL2h1bC9vaXMvamhvdmUvSW5mb01lc3NhZ2UuamF2YQ==) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openpreserve). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openpreserve)

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