RFR: 1658: Minimize race window when updating PR body [v5]

[Zhao Song]

> Currently, when the pr bot tries to update the PR body, users are also likely to update the PR body at the same time. Therefore, users' updates are likely to be overwritten by bot.  
> 
> This is a race between the bot and user and the race window is a little big right now.
> 
> To reduce the race window, in this patch, when PR bot is trying to update PR body, it will check whether the PR body has been modified by user. And if the PR bot has been modified, PR bot would not overwrite it.

Zhao Song has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge branch 'master' into SKARA-1658
   
   # Conflicts:
   #	bots/pr/src/test/java/org/openjdk/skara/bots/pr/CheckTests.java
   #	forge/src/main/java/org/openjdk/skara/forge/github/GitHubPullRequest.java
   #	forge/src/test/java/org/openjdk/skara/forge/github/GitHubRestApiTests.java
 - Merge branch 'master' into SKARA-1658
   
   # Conflicts:
   #	bots/pr/src/test/java/org/openjdk/skara/bots/pr/CheckTests.java
 - Merge branch 'master' into SKARA-1658
 - Added an automatic test for latestBody
 - SKARA-1658

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Changes: https://git.openjdk.org/skara/pull/1416/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1416&range=04
  Stats: 107 lines in 9 files changed: 104 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/skara/pull/1416.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1416/head:pull/1416

PR: https://git.openjdk.org/skara/pull/1416