Sync with 2.21.1

* maint-2.21: (42 commits)
  Git 2.21.1
  mingw: sh arguments need quoting in more circumstances
  mingw: fix quoting of empty arguments for `sh`
  mingw: use MSYS2 quoting even when spawning shell scripts
  mingw: detect when MSYS2's sh is to be spawned more robustly
  t7415: drop v2.20.x-specific work-around
  Git 2.20.2
  t7415: adjust test for dubiously-nested submodule gitdirs for v2.20.x
  Git 2.19.3
  Git 2.18.2
  Git 2.17.3
  Git 2.16.6
  test-drop-caches: use `has_dos_drive_prefix()`
  Git 2.15.4
  Git 2.14.6
  mingw: handle `subst`-ed "DOS drives"
  mingw: refuse to access paths with trailing spaces or periods
  mingw: refuse to access paths with illegal characters
  unpack-trees: let merged_entry() pass through do_add_entry()'s errors
  quote-stress-test: offer to test quoting arguments for MSYS2 sh
  ...

diff --cc Documentation/git-fast-import.txt
Simple merge

diff --cc Documentation/gitmodules.txt
Simple merge

diff --cc builtin/clone.c
Simple merge

diff --cc builtin/submodule--helper.c
Simple merge

diff --cc compat/mingw.c
Simple merge

diff --cc compat/mingw.h
Simple merge

diff --cc config.mak.uname
Simple merge

diff --cc connect.c
Simple merge

diff --cc fast-import.c
Simple merge

diff --cc fsck.c
index 4703f55561452c3fca5401aba3fcec7b170f1c6a,35bfb7f90e99ad43ab16d287c7414944bd94f9d3..fc4cb6ab910a0b06570a51edd7e041eb764d87b5
--- 1/fsck.c
--- 2/fsck.c
+++ b/fsck.c
@@@ -604,8 -605,8 +605,8 @@@ static int fsck_tree(struct tree *item
        o_name = NULL;
  
        while (desc.size) {
 -              unsigned mode;
 +              unsigned short mode;
-               const char *name;
+               const char *name, *backslash;
                const struct object_id *oid;
  
                oid = tree_entry_extract(&desc, &name, &mode);

diff --cc git-compat-util.h
Simple merge

diff --cc git-submodule.sh
index c7f58c5756f7b6f78689d574c5a2177d1bd409b5,f2d4d177b2330afbe7852bc6f5a80993b676f629..58713c5467f02dd79efefd4534373757af81713e
--- 1/git-submodule.sh
--- 2/git-submodule.sh
+++ b/git-submodule.sh
@@@ -548,9 -544,9 +553,10 @@@ cmd_update(
                ${reference:+"$reference"} \
                ${dissociate:+"--dissociate"} \
                ${depth:+--depth "$depth"} \
+               ${require_init:+--require-init} \
                $recommend_shallow \
                $jobs \
 +              -- \
                "$@" || echo "#unmatched" $?
        } | {
        err=

diff --cc path.c
Simple merge

diff --cc read-cache.c
Simple merge

diff --cc submodule-config.c
Simple merge

diff --cc submodule.c
Simple merge

diff --cc t/t1450-fsck.sh
Simple merge

diff --cc t/t7406-submodule-update.sh
Simple merge

diff --cc t/t9300-fast-import.sh
Simple merge

diff --cc transport-helper.c
index 6b05a88faf59ee74840b0f9fa340a5d9397a0f5d,d4683c4d0fb2c416e91c36229cf0e513e1639aea..f828a6da68f1b362e8ee2420de517541cebbfab6
--- 1/transport-helper.c
--- 2/transport-helper.c
+++ b/transport-helper.c
@@@ -423,8 -421,9 +423,9 @@@ static int get_importer(struct transpor
        struct helper_data *data = transport->data;
        int cat_blob_fd, code;
        child_process_init(fastimport);
 -      fastimport->in = helper->out;
 +      fastimport->in = xdup(helper->out);
        argv_array_push(&fastimport->args, "fast-import");
+       argv_array_push(&fastimport->args, "--allow-unsafe-features");
        argv_array_push(&fastimport->args, debug ? "--stats" : "--quiet");
  
        if (data->bidi_import) {

diff --cc tree-walk.c
Simple merge

diff --cc unpack-trees.c
Simple merge