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

Forgot to adjust a few things when the location types were introduced and documented.

This was quite fundamentally broken, not only due to previous change.

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.

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

Backwards compatibility is provided for vnd.dovecot.duplicate.
Still need to fix the constraint that it must not track duplicates from failed Sieve executions.

doc/extensions/spamtest-virustest.txt: Clarified that these extensions use the extended POSIX regular expressions.

Use sieve_vacation_send_from_recipient to enable this behavior.
Documentation in doc/extensions/vacation.txt is updated.

It is still a plugin, but no longer a separate package.

It is now possible to track duplicates based on arbitrary headers or even arbitrary string values using the new :header and :value arguments respectively.
The experation time can be configured using the new :seconds argument.
This change is backwards compatible as long as the name argument wasn't used. This is now a :handle <handle> argument.

Change backported from Pigeonhole v0.4 tree, which means that this change will duplicate there upon merge.

Added support for the :optional tag of the include command.
Changed Sieve script API in the process; opening the script is now available as a separate step.

sieve-refilter: improved man page documentation by explicitly specifying the syntax used for mailbox arguments.

Also fixed a small mistake in the spefication for the vnd.dovecot.duplicate extension.

This currently breaks uninstall when the settings plugins are removed and 20-managesieve.conf
remains in conf.d directory. These sections only need to be active in the config file when settings
for the services themselves need to be disabled.

Incorporated sieve_duplicate plugin into main Pigeonhole tree as a normal extension (vnd.dovecot.duplicate).
Also restructured doc dir a bit in the process.