Merge branch 'stable-5.1' into stable-5.2

Merge branch 'stable-5.1' into stable-5.2

* stable-5.1:
  Prepare 5.1.12-SNAPSHOT builds
  JGit v5.1.11.201909031202-r
  Prepare 4.11.10-SNAPSHOT builds
  JGit v4.11.9.201909030838-r
  Bazel: Update bazlets to the latest master revision
  Bazel: Remove FileTreeIteratorWithTimeControl from BUILD file
  BatchRefUpdate: repro racy atomic update, and fix it
  Delete unused FileTreeIteratorWithTimeControl
  Fix RacyGitTests#testRacyGitDetection
  Change RacyGitTests to create a racy git situation in a stable way
  Silence API warnings

Change-Id: Iac5dc9683cea97db04d20f27c10f2e103d3ae7b5
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>