Avoid using a Sieve error handler directly.

lib-sieve: sieve-error - Compose both the event and the error handler log message once using the event API.

Before, it used format string and arguments.

sieve-tools: sieve-test - Use the new result message amendment callback rather than the prefix error handler.

sieve-tools: sieve-filter - Use the new result message amendment callback rather than the prefix error handler.

plugins: lda-sieve: Use the new result message amendment callback rather than a special error handler.

Before it always used the name of the action definition, which is confusing e.g.
for the keep and fileinto actions, which both map to the same "store" action
definition.

This allows logging action messages through a different (child) event.

Applies to Sieve actions being executed.

Applies to Sieve scripts being evaluated before the actual action execution.

Applies to Sieve scripts being executed in general.

Always associate a pool with the execute context.

lib-sieve: sieve-result - Make direct result pointer avalable as local variable in sieve_result_unref().

This allows passing error parameters struct from sieve_critical*().

It is no longer used.

This prevents segfaults e.g. when dovecot/lib wants to log errors at
lib_deinit().

Trying to get them as shared instead of as private resulted in failure.