lib-mail: Forgot to commit .h file for message_decoder_current_content_type() change.

Replaced "decomposed titlecase" conversions with more generic normalizer function. Plugins can now change mail_user.default_normalizer. Specific searches can also use different normalizers by changing mail_search_context.normalizer.

lib-mail: Added message_decoder_parse_cte()

lib-mail: Added message_decoder_set_return_binary()

message-decoder now supports optionally returning non-text bodyparts as-is. --HG-- branch : HEAD

Message decoding wasn't reset properly between messages when searching. --HG-- branch : HEAD

Changed .h ifdef/defines to use <NAME>_H format. --HG-- branch : HEAD

Renamed ucase parameters to dtcase which is more correct. --HG-- branch : HEAD

Changed message_decoder_init_ucase() to message_decoder_init(bool ucase) --HG-- branch : HEAD

Renamed message_decoder_init() to message_decoder_init_ucase() and changed it to uppercase all the output. --HG-- branch : HEAD

Added message-decoder to decode message's contents into readable UTF-8. --HG-- branch : HEAD