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.

This allows performing ManageSieve actions at command line or through doveadm server.

lib-sieve: file storage: Restructured storage initialization to address backwards compatibility issues.

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.

It had a whitespace where it didn't belong.

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

Also added testsuite items to test syntax.

lib-sieve: Flush duplicate database during start phase of result execution rather than commit phase.
This will release the duplicate database lock earlier, even before a mail storage transation is started.

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 the index stringlist class which selects an item of the parent at a particular index.