Support parsing email addresses from SANs

[richcybermyte]

Most US Government organizations do not put the email address where Thunderbird expects, thus, I can not import a government certificate and encrypt email to the sender. The email address is actually kept in the Subject Alternative Name: email: field. for example:

```

X509v3 Extended Key Usage:
    E-mail Protection, 1.3.6.1.4.1.311.10.3.12, 1.2.840.113583.1.1.5
X509v3 Subject Alternative Name:
    email:some.one@someorg.gov
X509v3 CRL Distribution Points:
     Full Name:

```

A normal certificate from ssl.com or where ever you get your smime certs from, the email address is listed in the Subject and the SAN.

The enhancement would allow a user to sign and encrypt emails to the 3 million US Government workforce.

[Jon]

Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.

[wsm]

SAN should already work. If it does not, please file a bug report with a sample email certificate.  Thanks.