Merge branch 'stable-5.1'

Merge branch 'stable-5.1'

* stable-5.1:
  Fix NoSuchFileException during directory cleanup in RefDirectory
  Update japicmp to 0.13.0
  Prepare 5.1.1-SNAPSHOT builds
  JGit v5.1.0.201809111528-r
  Externalize warning message in RefDirectory.delete()
  Suppress warning for trying to delete non-empty directory
  Fix replacement quoting for replaceAll in filter command
  Prepare 4.11.3-SNAPSHOT builds
  JGit v4.11.2.201809100523-r

Change-Id: Ia27fec6dabf87db26e2fd29c17570932649e234a
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>