#66 Question mark in subject corrupts subject

[Amiram]

When MailMessage.Charset is used (e.g. "Windows-
1255") and the subject contains a question mark, the
subject gets corrupted. The reason is probably that
when Charset is needed, strings are surrounded by
question marks and embedded question marks should
receive special treatment.

[Chan]

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user_id=1370840

This is due to a non-compliance to RFC1521 and RFC1522.

First, the quoted-printable encoding is different from
RFC1521 when used in the headers, as stated in RFC1522
(spaces should be encoded as underscores, question marks and
underscores as =XX, and so on...).

Second, when there is a line feed in a header value (this is
the case for a long quoted-printable encoded subject), each
additional line should begin with a tab or a space (RFC
1521) to be differenciated from the folowing headers.

Fix these two bugs, and it'll be ok.