Merge branch 'nd/files-backend-git-dir'

The "submodule" specific field in the ref_store structure is
replaced with a more generic "gitdir" that can later be used also
when dealing with ref_store that represents the set of refs visible
from the other worktrees.

* nd/files-backend-git-dir: (28 commits)
refs.h: add a note about sorting order of for_each_ref_*
t1406: new tests for submodule ref store
t1405: some basic tests on main ref store
t/helper: add test-ref-store to test ref-store functions
refs: delete pack_refs() in favor of refs_pack_refs()
files-backend: avoid ref api targeting main ref store
refs: new transaction related ref-store api
refs: add new ref-store api
refs: rename get_ref_store() to get_submodule_ref_store() and make it public
files-backend: replace submodule_allowed check in files_downcast()
refs: move submodule code out of files-backend.c
path.c: move some code out of strbuf_git_path_submodule()
refs.c: make get_main_ref_store() public and use it
refs.c: kill register_ref_store(), add register_submodule_ref_store()
refs.c: flatten get_ref_store() a bit
refs: rename lookup_ref_store() to lookup_submodule_ref_store()
refs.c: introduce get_main_ref_store()
files-backend: remove the use of git_path()
files-backend: add and use files_ref_path()
files-backend: add and use files_reflog_path()
...

diff --cc Makefile
Simple merge

diff --cc path.c
Simple merge

diff --cc refs.c
Simple merge

diff --cc submodule.c
Simple merge

diff --cc submodule.h
index 486371d2c34a9397d9f075f052cbae774ad662e7,fce2fb64d2c6100903d9c1ce1c746a36de08d36c..1277480add48140c6bf8c6cbc51cb962e27637ae
--- 1/submodule.h
--- 2/submodule.h
+++ b/submodule.h
@@@ -98,14 -81,13 +98,20 @@@ extern int push_unpushed_submodules(str
                                    int dry_run);
  extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
  extern int parallel_submodules(void);
+ /*
+  * Given a submodule path (as in the index), return the repository
+  * path of that submodule in 'buf'. Return -1 on error or when the
+  * submodule is not initialized.
+  */
+ int submodule_to_gitdir(struct strbuf *buf, const char *submodule);
  
 +#define SUBMODULE_MOVE_HEAD_DRY_RUN (1<<0)
 +#define SUBMODULE_MOVE_HEAD_FORCE   (1<<1)
 +extern int submodule_move_head(const char *path,
 +                             const char *old,
 +                             const char *new,
 +                             unsigned flags);
 +
  /*
   * Prepare the "env_array" parameter of a "struct child_process" for executing
   * a submodule by clearing any repo-specific envirionment variables, but

diff --cc t/helper/.gitignore
Simple merge