Add the --noreply option to 'mail'

There are mailing lists (ARM Linux Kernel is one of them) that filter out
e-mails having the In-Reply-To: header but a subject line not starting with
Re:. With this option, the mail command will not create the reply-specific
headers (the patch series will be unthreaded).

Signed-off-by: Catalin Marinas <catalin.marinas@gmail.com>