Fix AddressList toString method to quote semicolon

[weierophinney]

Certain input of AddressList headers, cannot be converted to string and back to header object because of incorrect quoting:

From: "Foo;" <root@example.com>

gets incorrectly converted as

From: Foo; <root@example.com>

but ; is address separator, so it needs to be quoted:

From: "Foo;" <root@example.com>

The problem I discovered internally when using Storage\Message with Headers input, therefore testing that method is included in the unit test:

$message = new Message(['headers' => new Headers(), 'content' => (string)$body]);

// Mime\Decode::splitMessage calls toString on headers object which creates invalid result:
if ($message instanceof Headers) {
    $message = $message->toString();
}

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Originally posted by @glensc at zendframework/zend-mail#230

[weierophinney]

@weierophinney, @Xerkus can you take care of this?

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Originally posted by @glensc at zendframework/zend-mail#230 (comment)

[weierophinney]

this is a regression from #147 as it added ; separator support that's why (i believe) this exception is caught.

however, there should not be an assumption that only zend-mail is used for reading writing mail messages.

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Originally posted by @glensc at zendframework/zend-mail#230 (comment)