Merge branch 'mv/merge-recursive'

Merge branch 'mv/merge-recursive'

* mv/merge-recursive:
  builtin-merge: release the lockfile in try_merge_strategy()
  merge-recursive: get rid of virtual_id
  merge-recursive: move current_{file,directory}_set to struct merge_options
  merge-recursive: move the global obuf to struct merge_options
  merge-recursive: get rid of the index_only global variable
  merge-recursive: move call_depth to struct merge_options
  cherry-pick/revert: make direct internal call to merge_tree()
  builtin-merge: avoid run_command_v_opt() for recursive and subtree
  merge-recursive: introduce merge_options
  merge-recursive.c: Add more generic merge_recursive_generic()
  Split out merge_recursive() to merge-recursive.c