branch: stop modifying log_all_ref_updates variable

In "branch.c" we modify the global `log_all_ref_updates` variable to
force creation of a reflog entry. Modifying global state like this is
discouraged, as it may have all kinds of consequences in other places of
our codebase.

Stop modifying the variable and pass the `REF_FORCE_CREATE_REFLOG` flag
instead. Setting this flag has a stronger meaning than setting the
config to `LOG_REFS_NORMAL`:

  - `LOG_REFS_NORMAL` will ask us to only create reflog entries for
    preexisting reflogs or branches, remote refs, note refs and HEAD.

  - `REF_FORCE_CREATE_REFLOG` will unconditionally create a reflog and
    is thus equivalent to `LOG_REFS_ALWAYS`.

But as we are in `create_branch()` and thus do not have to worry about
arbitrary references, but only about branches, `LOG_REFS_NORMAL` and
`LOG_REFS_ALWAYS` are indeed equivalent.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

branch.c

@@ -601,6 +601,7 @@ void create_branch(struct repository *r,
 	int forcing = 0;
 	struct ref_transaction *transaction;
 	struct strbuf err = STRBUF_INIT;
+	int flags = 0;
 	char *msg;
 
 	if (track == BRANCH_TRACK_OVERRIDE)
@@ -619,7 +620,7 @@ void create_branch(struct repository *r,
 		goto cleanup;
 
 	if (reflog)
-		log_all_ref_updates = LOG_REFS_NORMAL;
+		flags |= REF_FORCE_CREATE_REFLOG;
 
 	if (forcing)
 		msg = xstrfmt("branch: Reset to %s", start_name);
@@ -630,7 +631,7 @@ void create_branch(struct repository *r,
 	if (!transaction ||
 		ref_transaction_update(transaction, ref.buf,
 					&oid, forcing ? NULL : null_oid(),
-					NULL, NULL, 0, msg, &err) ||
+					NULL, NULL, flags, msg, &err) ||
 		ref_transaction_commit(transaction, &err))
 		die("%s", err.buf);
 	ref_transaction_free(transaction);