Testsuite failed with an assertion, because the stream returned -2 at an unexpected time.
I've restructured the buffering implementation to prevent this.
The testsuite succeeds now, but this needs to be tested more thoroughly.

Also contains a few other small fixes by Timo.

lib-sieve: increase action instance count (for limit checking) only when an action is actually created.

Sieve script equality function implementation was wrong.

Patch by Eray Aslan.

Patch by Timo Sirainen.

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

Clang static analyzer is happy now.

Additional paths are specified by adding a sequence number (starting at 2) to the setting name.
Added support for specifying home-relative paths for sieve_before and sieve_after.
This enables administrators to specify user-specific global Sieve scripts that cannot be viewed or changed by virtual users.

Fixed segfault bug. Forgot to change Sieve SMTP API to use scriptenv in stead of script_context directly.

  - Built generic interface for alternative script sources.
  - Implemented dict script location.
  NOTE: ManageSieve will not work with this yet, nor will sieve_before/sieve_after.

Fixes behavior of body test with multipart MIME body parts.
Testsuite needs to be extended accordingly.

Setting sieve_max_redirects=0 now means that redirects are prohibited rather than unlimited.
Now there is always a limit, but it can be enormous if the administrator wants to.

Message substitutions would not always cause a proper snapshot.

This is needed for the new extprograms plugin.

Removes quite a bit of duplicated source code.

This puts the ".sieve" and ".svbin" file extension definitions in a single locatio.
IMPORTANT: this fixes a bug in the include extension that implicitly mapped script names like "name.sieve" to "name".

Upon upload, the include extension is more lenient towards circular includes and missing scripts as required by RFC.
The script is now also verified upon SETACTIVE when it was not active before.
However, this new SETACTIVE behavior is not optimal for the situation where the active script was updated with
PUTSCRIPT and contains an nonexistent include (ignored during upload). This can still cause runtime errors, since
an already active script is not verified again during SETACTIVE.