Providing an out-of-range index caused an assert panic.

Panic was:

Panic: file mail-index-transaction-update.c: line 19 (mail_index_transaction_lookup): assertion failed: (seq >= t->first_new_seq && seq <= t->last_new_seq)

Fixes assert failure occurring either at compiletime or at runtime (depending on
whether the value originates from variable).

Fixes assert failure occurring at runtime (when value originates from variable).

Compile error is avoided by putting the mailbox name in a variable, which is
(currently) only evaluated at runtime.

Before, it would only terminate the test when it failed explicitly using the
test_fail command.

This holds a reference to the initial result, causing it to linger after
test_result_reset, thereby also holding a reference to the message context,
preventing it from being cleared. This in turn, can keep references to modified
message versions that cause the main message object to remain referenced. This
causes a panic in specific cases upon test_result_reset:

Panic: Input stream data unexpectedly has references

Caused a panic when input was not valid. This is only relevant to the test suite
and doesn't occur anywhere else (apart from the previous similar commit for
lib-sieve-tool).

Panic was:

Panic in file smtp-address.c: line 684 (smtp_address_write): assertion failed: (smtp_char_is_qpair(*p))`

The segfault happens when this match type is the last argument of the test
command. This situation is not possible in a valid script; positional arguments
are normally present after that, which would prevent the segfault. A variant of
this bug occurs when the match type also has no argument of its own. In either
case the segfault is caused by referring to absent tag arguments, which causes
a NULL dereference.

The use of a variable substitution erroneously produced a runtime syntax error.

Also check the X-Sieve-Redirected-From header for our own e-mail addresses. This
header is added by the redirect action itself and in a mail loop it would see
that same header with that same content. This is less reliable than the other
mail loop detection (sender may set such a header), so, unlike the existing loop
detection based on the duplicate db, the implicit keep is not canceled when the
new loop detection is triggered.

test suite: enotify extension: Add tests for interaction between ":encodeurl" and variable size limits.

It is a remnant from debugging.

It erroneously applied another layer of MIME header encoding.
The problem is that existing Sieve scripts may rely on this behaviour; i.e. scripts may contain addresesses with literal UTF8 in the phrase part.
Therefore, this change allows both behaviors.

Now using struct smtp_address rather than sieve_address.
In some cases, struct message_address may prove to be more suitable, but this is the best fit for now.
Adjusted to the renamed fields in struct mail_deliver_context.

lib-sieve: redirect action: Always set X-Sieve-Redirected-From header to sieve_user_email if configured.

Set it to the final recipient only when there is an envelope and sieve_user_email is unconfigured.

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.

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.

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.