Merge branch 'jk/consistent-h'

"git $cmd -h" for builtin commands calls the implementation of the
command (i.e. cmd_$cmd() function) without doing any repository
set-up, and the commands that expect RUN_SETUP is done by the Git
potty needs to be prepared to show the help text without barfing.

* jk/consistent-h:
  t0012: test "-h" with builtins
  git: add hidden --list-builtins option
  version: convert to parse-options
  diff- and log- family: handle "git cmd -h" early
  submodule--helper: show usage for "-h"
  remote-{ext,fd}: print usage message on invalid arguments
  upload-archive: handle "-h" option early
  credential: handle invalid arguments earlier

builtin/diff-files.c

@@ -20,6 +20,9 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 	int result;
 	unsigned options = 0;
 
+	if (argc == 2 && !strcmp(argv[1], "-h"))
+		usage(diff_files_usage);
+
 	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 	init_revisions(&rev, prefix);
 	gitmodules_config();