lib-sieve: vacation extension: Use Microsoft X-Auto-Response-Suppress header to prevent unwanted responses.

We've seen a few situations where Pigeonhole and Microsoft products start a useless machine conversation.
At least older versions of Outlook ignore the standards on multiple points to make this happen.
We prevent this now by recognizing and generating the X-Auto-Response-Suppress header.

lib-sieve: vnd.dovecot.report extension: Added Dovecot-Reporting-User field, which contains the e-mail address of the user sending the report.

lib-sieve: vnd.dovecot.report extension: Added support for configuring the "From:" address used in the report.

A "vnd.dovecot.config.<identifier>" environment item maps to the content of the matching sieve_env_<identifier> plugin setting.

lib-sieve: vacation extension: The sieve_user_email setting is now used in check for implicit delivery.

This means that vacation responses are now also sent for messages that include the sieve_user_email address in one of the relevant headers.

The recipient_delimiter is treated as multiple one-character delimiters
rather than one multi-character delimiter if more than one character is
supplied.

Based on a patch by: Lennart Weller <lhw@ring0.de>

This is used mainly when no other means of obtaining the user's email is available, such as when there is no envelope (in IMAP).
Before, the postmaster address or the null "<>" address was used as a fallback for sending messages.
The redirect and enotify commands can be explicitly configured to use what is configured with sieve_user_email.

lib-sieve: Made sure local part of a mail address is encoded properly using quoted string when it is not a dot-atom.

Registering conflicting commands before conflicts are checked is a bad idea.
Make sure conflicting extensions are not part of remaining validation process.

It allows sending feedback report (RFC 5965) messages.

lib-sieve: util: program-client-local: Changed link between parent and child process from a socketpair to a double pipe.

Turns out /dev/stdin, /dev/stdout, and /dev/fd/XX don't work on Linux if the underlying FD is a socket.
Since some programs may rely on those symbolic links to work, the local client is amended to use two pipes instead.
This will not help for programs invoked in the remote script service, since a socket is required for the connection.

Fixed a few printf format problems in the process.
Updated test suite to account for the new number width.

lib-sieve: multiscript: Fixed bug in handling of (implicit) keep; final keep action was executed as though there was a failure.
Among other things, this caused the keep action to revert back to the initial message, causing editheader actions to be ignored.

lib-sieve: mime extension: Fixed the header :mime :anychild test to work properly outside a foreverypart loop.

test suite: mime extension: Improved header test cases to catch header trimming and folding problems.

lib-sieve: message body: Fixed assert failure occurring when text extraction is attempted on a empty or broken text part.

Included scripts now execute in the context of the inner parent foreverypart loop.

An empty string yielded an empty string rather than "0".

It now extracts bare text from HTML/XHMTL parts.
Other text/* parts are still returned as is. Any other unrecognized content types are skipped.

This allows setting the MAIL FROM of the SMTP envelope for the notification e-mails.
The syntax is identical to the sieve_redirect_envelope_from setting.

Sieve extprograms plugin: Made line endings configurable for the input passed to the external program.