__gitcomp takes care of it since 5447aac7 (bash: fix long option with
argument double completion, 2008-03-05)
Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>