Add support for unicode characters in domain, username and password

Hi Mike,

I recently ran into unicode-related issues when logging usernames containing Japanese characters in the python2 version of `smb.base.SMB.__init__()` . This patch fixes the issue.

For our tests we used username `ユーザ名` and password `パスワード`. These were utf8-encoded into byte strings, and then url-encoded using urllib2.quote() to create the smb URL `smb://%E3%83%A6%E3%83%BC%E3%82%B6%E5%90%8D:%E3%83%91%E3%82%B9%E3%83%AF%E3%83%BC%E3%83%89@<windows-server>:139`

Regards,
Andy