Eclipse JGit: Java implementation of Git 5.6.1

Monitoring enhancements

• 553573 WindowCache: add metric for cached bytes per repository
• 553573 WindowCache: add option to use strong refs to reference ByteWindows
  
  Set core.packedGitUseStrongRefs = true to enable using strong references to reference packfile pages cached in the WindowCache. If this option is set Java gc can no longer flush the WindowCache to free memory if the used heap comes close to the maximum heap size. On the other hand this provides more predictable performance.
• 553573 Enhance WindowCache statistics
• Add config constants for WindowCache configuration options

Performance improvements

• Replace usage of ArrayIndexOutOfBoundsException in treewalk

Bug Fixes

• Simplify ReftableCompactor
• reftable: don't check deadline on the first try
• reftable: clear cache on full compaction
• 559796 Restore behavior of CloneCommand to configure fetch refspec with wildcards
• 558577 Hooks: avoid problems with backslashes in paths
• Fix MBean registration
• pgm daemon: fallback to user and system config if no config specified
• SshSupport#runSshCommand: don't throw exception in finally block

Build and Release Engineering

• Bump required Bazel version to 2.1.0
• Upgrade bazlets to the latest master revision
• Don't override already managed maven-compiler-plugin version
• Remove duplicate ignore_optional_problems entry in .classpath
• Update maven-site-plugin used by benchmark module to 3.8.2
• Add dependency to enable site generation for benchmark module
• Ignore warnings for generated source code in org.eclipse.jgit.benchmark