RFC 2822 allows for comments to include other comments
in a mail address. email.Utils.getaddresses() handled
addresses with a comment, but incorrectly advanced the
parsing index twice after a comment finished. This
would cause the outer closing paren in an address like:
    Foo ((FOO Rocks)) <foo@bar.com>
to be missed, and treating the rest of the line as part
of the outer comment.

This patch fixes the bug and adds a testcase to look
for the bug.