Merge branch 'js/early-config' into maint

Correct start-up sequence so that a repository could be placed
immediately under the root directory again (which was broken at
around Git 2.13).

* js/early-config:
  setup: avoid double slashes when looking for HEAD

setup.c

@@ -312,7 +312,9 @@ int is_git_directory(const char *suspect)
 	size_t len;
 
 	/* Check worktree-related signatures */
-	strbuf_addf(&path, "%s/HEAD", suspect);
+	strbuf_addstr(&path, suspect);
+	strbuf_complete(&path, '/');
+	strbuf_addstr(&path, "HEAD");
 	if (validate_headref(path.buf))
 		goto done;