Merge branch 'mv/merge-in-c'

Merge branch 'mv/merge-in-c'

* mv/merge-in-c:
  reduce_heads(): protect from duplicate input
  reduce_heads(): thinkofix
  Add a new test for git-merge-resolve
  t6021: add a new test for git-merge-resolve
  Teach merge.log to "git-merge" again
  Build in merge
  Fix t7601-merge-pull-config.sh on AIX
  git-commit-tree: make it usable from other builtins
  Add new test case to ensure git-merge prepends the custom merge message
  Add new test case to ensure git-merge reduces octopus parents when possible
  Introduce reduce_heads()
  Introduce get_merge_bases_many()
  Add new test to ensure git-merge handles more than 25 refs.
  Introduce get_octopus_merge_bases() in commit.c
  git-fmt-merge-msg: make it usable from other builtins
  Move read_cache_unmerged() to read-cache.c
  Add new test to ensure git-merge handles pull.twohead and pull.octopus
  Move parse-options's skip_prefix() to git-compat-util.h
  Move commit_list_count() to commit.c
  Move split_cmdline() to alias.c

Conflicts:
	Makefile
	parse-options.c