wrapper: use a loop instead of repetitive statements

wrapper: use a loop instead of repetitive statements

A check into the history of this code revealed no particular reason for
the code to be written in this way. All popular compilers are capable of
unrolling loops if it benefits performance, and once this code is
replaced with a loop, the magic number 6 used in multiple places in this
function can be replaced with a named constant.

Reviewed-by: Derrick Stolee <stolee@gmail.com>
Reviewed-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>