Merge branch 'jk/date-mode-format'

Teach "git log" and friends a new "--date=format:..." option to
format timestamps using system's strftime(3).

* jk/date-mode-format:
  strbuf: make strbuf_addftime more robust
  introduce "format" date-mode
  convert "enum date_mode" into a struct
  show-branch: use DATE_RELATIVE instead of magic number

archive.c

@@ -34,7 +34,7 @@ static void format_subst(const struct commit *commit,
 	char *to_free = NULL;
 	struct strbuf fmt = STRBUF_INIT;
 	struct pretty_print_context ctx = {0};
-	ctx.date_mode = DATE_NORMAL;
+	ctx.date_mode.type = DATE_NORMAL;
 	ctx.abbrev = DEFAULT_ABBREV;
 
 	if (src == buf->buf)