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

commit.h

@@ -145,7 +145,7 @@ struct pretty_print_context {
 	const char *subject;
 	const char *after_subject;
 	int preserve_subject;
-	enum date_mode date_mode;
+	struct date_mode date_mode;
 	unsigned date_mode_explicit:1;
 	int need_8bit_cte;
 	char *notes_message;