lib-sieve: vacation extension: Allow ignoring the envelope sender while composing the "To:" header for the reply.

This adds a new setting "sieve_vacation_to_header_ignore_envelope".
With this setting enabled, the "To:" header is always composed from the first "Sender", "Resent-From" or "From" header found in the message (in that order).
Normally, the "To:" header is composed from the address found in the "Sender", "Resent-From" or "From" headers that is equal to the envelope sender.
If none is then found, the bare envelope sender is used.
The new setting allows ignoring the envelope, which is useful e.g. when SRS is used.

The sequence was broken when the LDAP script attribute does not exist; i.e., when the script is not found.
The NOT_FOUND error is returned at a later instance than normal fs-based scripts, explaining why this problem does not normally occur.

LDA Sieve plugin: Restructured execution of scripts by putting execution of individual scripts in separate function.

This is needed to register the implicit side effect for the internal flag variable.

The Dovecot API was changed years ago, but apparently sieve-filter was never updated.

imapsieve plugin: Provide proper error details upon failure to access the mailbox/server script METADATA attribute.

This addresses an old FIXME.

lib-sieve: vacation extension: Compose the "To:" header from full sender address found in the first "Sender:", "From:" or "Resent-From:" header.

Before, it would create a "To:" header without a phrase part. The new behavior is nicer, since the reply will be addressed to the sender by name if possible.
This addresses an old FIXME.

Only the first header is ever of interest.

Normally, this would merely be an inconsequential memory leak.
However, when the script comes from an LDAP storage, the storage is not closed before master_service_deinit() -> io_loop_destroy().
The LDAP connection's stale io can cause problems while closing the main ioloop.

Rather than continuing with binary == NULL, causing a segfault.

Commands that continued after waiting for more input always failed.
This mainly applies to the AUTHENTICATE command, which mostly handles its own arguments.
This caused problems when a string literal was used as the initial response for the AUTHENTICATE command.

Caused by recent change:

Author: Timo Sirainen <timo.sirainen@dovecot.fi>
Date:   Wed Jun 14 12:39:02 2017 +0300

managesieve-login: managesieve_client_input_next_cmd() - minor code cleanup

managesieve-login: authenticate command: Make sure client->auth_mech_name_parsed is reset properly upon command error.

This could cause problems for any subsequent AUTHENTICATE commmend.

Moved script cleanup to separate function as well.

lib-sieve: include extension: Fixed segfault that (sometimes) occurred when the global script location was left unconfigured.

For accounts that perform many redirects, the lda-dupes database could grow to impractical sizes.
Changed the default retention period from 24 to 12 hours.

Upon continuing the deferred implicit keep, the implicit side-effects (such as imap flags) were not applied.

Implicit keep was deferred for the source message, which discards all flags.

When this is enabled for a mailbox rule, the specified Sieve script is executed for the message in the source mailbox during a "COPY" event.
This happens only after the Sieve script that is executed for the corresponding message in the destination mailbox finishes running successfully.

This already has the imapsieve transaction context associated with it before the sieve scripts are executed.
This currently cannot occur, but it will become relevant in subsequent commits.

imapsieve plugin: Don't open the user's personal script storage if no personal script is configured.

lib-sieve: multiscript: The execution of the discard script had an implicit "keep", rather than an implicit "discard".

lib-sieve: store action: Made static analyzer happier about tr_context argument for sieve_act_store_add_flags().

Added an assert ensuring it is not NULL.

This used strftime() directly and allocated memory from the heap before i_fatal().
It also used printf() to send the BYE message, which will only work right when the service is running stand-alone.