send-email: add test for Linux's get_maintainer.pl

send-email: add test for Linux's get_maintainer.pl

We had a regression that broke Linux's get_maintainer.pl. Using
Mail::Address to parse email addresses fixed it, but let's protect
against future regressions.

Note that we need --cc-cmd to be relative because this option doesn't
accept spaces in script names (probably to allow --cc-cmd="executable
--option"), while --smtp-server needs to be absolute.

Patch-edited-by: Matthieu Moy <git@matthieu-moy.fr>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Matthieu Moy <git@matthieu-moy.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>