* src/common.c (get_tmp_outfile): Add SHARE_DELETE
* src/mail.cpp (get_attachment, get_cipherstream),
(get_attachment_stream): Split get_cipherstream in two subfunctions.
(copy_data_property): Add disabled experimental code.
(copy_attachment_to_file): Copy attachment data to tmp file.
(add_attachments): Use copy to file.
(Mail::decrypt_verify): Update call according to new function.