DKIM / OpenDKIM Fixes

Hello,

While Working with Andrei Harry, i spotted a flaw in the signedMessage implementation, it basically does not allows the examples on swiftmailer.org to works while being signed in dkim / dk

+ some fixes on openssl_errors being muted instead of being thrown
+ removed an useless file (the extension was never made available), 
and i'm working on the new implementation using libopendkim.