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.

lib-sieve: util: program client: Fixed handing of situation when no input is provided to external program used as a command.
Previous fixes still omitted a few important aspects:
Connect return result wasn't actually passed up to program_client_run().
Default exit code was wrong.

lib-sieve: editheader extension: Made protection against addition and deletion of headers configurable separately.
Also, the received and auto-submitted headers are now only protected against deletion as required in the RFC.
Updated the documentation accordingly.

Currently cannot freely assing server metadata items for testing.
Disabled tests for now.

lib-sieve: Fixed bug in `:matches' match-type that made a pattern without wildcards match as if there were a '*' at the beginning.

It couldn't handle a missing parameter (which also means missing arguments of the test itself in most cases).
This is fixed by using the sieve_validate_tag_parameter() utility function.
Testsuite is also extended.

Recent changes in handling of unknown tags caused `make test-plugins' to fail.

Also added testsuite items to test syntax.

This allows extension of test commands that evaluate the message somehow.
Currently this is implemented only for the message header.
Extensions can thereby influence what headers are evaluated and how.

lib-sieve: Implemented sieve_redirect_envelope_from setting, which allows configuring the envelope sender of redirected messages.
Can either be set to the envelope sender, recipient, or orignal recipient of the processed message or it can be set explicitly to a static address.

Based on patch by Timo Sirainen.

Doveadm-sieve plugin may be broken at this point; not tested so far.