Merge branch 'mw/alternates' into next

Merge branch 'mw/alternates' into next

* mw/alternates:
  clone: don't clone the info/alternates file
  test case for transitive info/alternates
  Transitively read alternatives
  repack: honor -d even when no new pack was created
  clone: keep --reference even with -l -s
  repo-config: document what value_regexp does a bit more clearly.
  Release config lock if the regex is invalid
  core-tutorial.txt: escape asterisk
  Sparse fix for builtin-diff
  Fix users of prefix_path() to free() only when necessary