Merge branch 'stable-5.1' into stable-5.2

* stable-5.1:
  Prepare 5.1.11-SNAPSHOT builds
  JGit v5.1.10.201908230655-r
  Use AtomicReferences to cache user and system level configs
  Fix copy-paste typo in CloneCommand#cleanup

Change-Id: Ie383633de334e65901ed4c6deb2d59cfcce98e16

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/api/CloneCommand.java
Simple merge