follow RFC-6120 section 6.4.4: send <abord> and a SASL authentication mechanism fails, wait for server <failure> reply before trying a new mechanism

check DIGEST-MD% and SCRAM-SHA-1 latest answer from server before accepting authentication. Fixes #6940

Also use sed to remove now unneeded Vim lines, 2to3 -f ws_comma to fix
some whitespace, and fix some other madness manually.

fix insecure_connection text to not talk about password, and add new warning to inform user when he is about to send plain password on plain connection. Fixes #5607

also use 2to3 -f ws_comma to fix some whitespace

holy diff batman!

[Dave Cridland] try to encode username, realm and password in iso-8859-1 when doing DIGEST-MD5 before computing the hash. Fixes #5512

request connection password only when neede. No need to request it for GSSAPI or ANONYMOUS login. see #2465