try fixing crashes when sending messages: my gcc 2.95.4 seems
to generate bad code for 'send_send_data_progressive': When
called from 'send_send_data_finished', the 'data' pointer is
cleared just before the assignment to the dialog pointer
* doc-src/readme.txt
* doc-src/rfc2554.txt
add RFC about SMTP AUTH
* src/send_message.c
* src/common/smtp.[ch]
add extra error code for authentication errors and
clear temporary password when this error occurs
(closes Bug 84 authentication failure while sending should
prompt for password again)