It is generally a bad idea to add a potentially unlimited string to a filename,
especially when it contains a mailbox name.

Dovecot core doesn't have copyright notices in header files.

lib-sieve: Added sieve_script_env_init() to initialize struct sieve_script_env from struct mail_user.

The "discard script" is run when the normal script sequence ends and the message is going to be discarded.

This way, imapsieve can show to which user.mailbox.uid the trace applies.

This was duplicated between the lda-sieve and imapsieve plugins.

lib-sieve: Implemented support for writing runtime trace output to a directory if it exists, much like Dovecot rawlog.

lib-sieve: Renamed sieve_runtime_flags to sieve_execute_flags and made these available to result execution.

lib-sieve: Moved handling of implicit keep during multiscript execution outside the script sequence itself.
Before, implicit keep was executed as part of the final script execution. This caused the implicit keep to be executed as part of that script, including global context.
This caused insignificant errors during delivery to be logged as errors in the administrator log when the last script is global.

LDA Sieve plugin: Changed error handling so that each action log message can have up-to-date time stamps.
This change matches a change in LDA that is aimed at logging timing statistics.

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

This change is bigger than I would have liked, so this needs to be tested more.

  - 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.

- Added sieve_global_extensions setting.