lib-mail: message_header_encode() now preserves folding whitespace This function could still use some cleaning up, but good enough for now.. Also it should try to minimize the encoded words, not necessarily encoding everything between the first and the last words that have to be encoded.

lib-mail: message_header_encode_[bq]() now explicitly takes the first line length parameter. So this change partially reverts the previous change, because message_header_encode() was actually internally relying on this behavior. The explicit parameter makes it clearer.

lib-mail: message_header_encode() no longer tries to lookup the first line's length from output string. This function is used only by Pigeonhole, which only uses it for empty output strings, so it's not useful there. Also that behavior is somewhat unexpected and confusing.

lib-mail: Added message_header_encode_data() to support encoding also NUL characters.

Added message header (RFC 2047) encoder. --HG-- branch : HEAD