Before further refactoring the "t0021/rot13-filter.pl" script,
let's modernize the style of its 'if .. elsif .. else' clauses
to improve its readability by making it more similar to our
other perl scripts.
Signed-off-by: Christian Couder <chriscool@tuxfamily.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>