Merge branch 'stable-6.0' into stable-6.1

* stable-6.0:
  Add pack options to preserve and prune old pack files
  Allow to perform PackedBatchRefUpdate without locking loose refs
  Document option "core.sha1Implementation" introduced in 59029aec

Change-Id: I876a38c2de8b7d5eaacd00e36b85599f88173221

diff --cc Documentation/config-options.md
Simple merge

diff --cc org.eclipse.jgit/.settings/.api_filters
Simple merge

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
index 4755693922e939b8c0f1d29571e4dde888fc8690,7d3430ffc577b2344c1453a58aea2eb61654980d..5c82f13787ce3c5534d9deec74271b0d300c21ec
--- 1/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
--- 2/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
@@@ -835,31 -771,18 +835,45 @@@ public final class ConfigConstants 
         */
        public static final String CONFIG_KEY_SEARCH_FOR_REUSE_TIMEOUT = "searchforreusetimeout";
  
 -
 +      /**
 +       * The "push" section.
 +       *
 +       * @since 6.1
 +       */
 +      public static final String CONFIG_PUSH_SECTION = "push";
 +
 +      /**
 +       * The "default" key.
 +       *
 +       * @since 6.1
 +       */
 +      public static final String CONFIG_KEY_DEFAULT = "default";
 +
 +      /**
 +       * The "abbrev" key
 +       *
 +       * @since 6.1
 +       */
 +      public static final String CONFIG_KEY_ABBREV = "abbrev";
 +
 +      /**
 +       * The "trustPackedRefsStat" key
 +       *
 +       * @since 6.1.1
 +       */
 +      public static final String CONFIG_KEY_TRUST_PACKED_REFS_STAT = "trustPackedRefsStat";
++
+       /**
+        * The "pack.preserveOldPacks" key
+        *
+        * @since 5.13.2
+        */
+       public static final String CONFIG_KEY_PRESERVE_OLD_PACKS = "preserveoldpacks";
+ 
+       /**
+        * The "pack.prunePreserved" key
+        *
+        * @since 5.13.2
+        */
+       public static final String CONFIG_KEY_PRUNE_PRESERVED = "prunepreserved";
  }