RFR: 2637: Decoding emails from quoted-printable is broken

[Erik Joelsson]

During my initial implementation of Mailman 3 support, I made an attempt at decoding quoted-printable encoded email bodies. That implementation isn't working that well. I only took 2 byte encoded UTF-8 characters into account, but we of course need to also handle 3 and 4 byte characters.

Instead of trying to do this with regular expressions, I bit the bullet and started working on a byte array, byte by byte. That actually makes it a lot simpler as we just need to translate each encoded triplet (`=XX`) at a time and then just convert the resulting byte array using Java's built in character set decoder.

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Commit messages:
 - comment
 - SKARA-2637

Changes: https://git.openjdk.org/skara/pull/1747/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1747&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2637
  Stats: 61 lines in 2 files changed: 43 ins; 8 del; 10 mod
  Patch: https://git.openjdk.org/skara/pull/1747.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1747/head:pull/1747

PR: https://git.openjdk.org/skara/pull/1747