RFR: 1669: Limit the amount of description copied into subsequent comment emails

[Zhao Song]

A user complains about that sometimes the pr body can be very long and this very long pr body will be included in every email about this pr. The user will need to scroll down many times to the bottom of the email to find the useful information.

In this patch, the length of **quoted** pr body or comment is limited to 2500.

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Commit messages:
 - SKARA-1669

Changes: https://git.openjdk.org/skara/pull/1511/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1511&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1669
  Stats: 99 lines in 2 files changed: 99 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/skara/pull/1511.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1511/head:pull/1511

PR: https://git.openjdk.org/skara/pull/1511