login-common API made more extensible for different kinds of protocols. Patch by Stephan Bosch.

imap-login: Fixed handling second AUTHENTICATE command when the first one failed.

imap-login: Handle SASL-IR without overflowing master_auth_request's buffer.

imap: imap_capability = +foo only adds new capabilities instead of replacing everything.

*-login: Moved most of the common code to login-common. --HG-- branch : HEAD

*-login: Use a common client_send_line() API. --HG-- branch : HEAD

login processes: Added initial support for per-connection configuration. --HG-- branch : HEAD

imap-login: Use [resp-codes] to figure out when to replace remote's auth failed message with ours. --HG-- branch : HEAD

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

Added more consts to imap-parser API --HG-- branch : HEAD

Added "bool" type and changed all ints that were used as booleans to bool. --HG-- branch : HEAD

disable_plaintext_auth defaults to yes now. ipv4 127.* and ipv6 ::1 addresses are considered secure however and plaintext authentication is allowed from them. --HG-- branch : HEAD

Don't advertise AUTH=PLAIN in capability if disable_plaintext_auth = yes and SSL/TLS is not yet negotiated. --HG-- branch : HEAD

Moved common login process code to login-common, created pop3-login. --HG-- branch : HEAD