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

diff --cc Makefile
Simple merge

diff --cc builtin-checkout.c
Simple merge

diff --cc builtin-merge.c
Simple merge

diff --cc t/t6026-merge-attr.sh
Simple merge