dsync: When full resync is wanted in a stateful sync, output empty state. This continues 3d49dc64d, which didn't actually work because brain->require_full_resync was either cleared earlier or it was never even set in this brain.

global: unsigned int:1 -> bool:1 perl -i -pe 's/unsigned int ([^,:;]+):1;/bool $1:1;/' **/*.[ch]

dsync: Use storage's mail_error to choose the doveadm exit code. Instead of always assuming that all errors are EX_TEMPFAIL.

dsync: Added an extra "finish" state to allow slave-dsync to report error to master-dsync. I'm not sure if that's actually necessary, but just trying to follow the different possibilities on how dsync run can finish made me unsure about it. This should make it at least clear that if a slave-dsync has a failure flag set at deinit master-dsync will know about it before it returns success.

dsync: Fixed talking to earlier dsync without mailbox attribute support. Most importantly it can now be used as an example how to add more features to dsync.

dsync: Added support for syncing mailbox attributes.

dsync: If I/O gets stalled, log the state in which it happened.

dsync: Close mail streams earlier on failures to avoid assert-crashing

dsync: Fixes to handling output stream buffering.

dsync: Renamed "slave" to "ibc" (= inter-brain communicator)