connect: address -Wsign-compare warnings

connect: address -Wsign-compare warnings

Most of the warnings were about loop variables being declared as ints
with a condition using a size_t, whereby switching the variable to
size_t fixes the warning.

One other case was comparing the result of strlen to an int passed
as an argument, which turns out could just as well be passed as a
size_t, albeit trickling to other functions.

Signed-off-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>