add storage size output to 'git verify-pack -v'

add storage size output to 'git verify-pack -v'

This can possibly break external scripts that depend on the previous
output, but those script can't possibly be critical to Git usage, and
fixing them should be trivial.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>