introduce recognition of $USE_VALGRIND to run all mbsync invocations
through valgrind.
this also removes the seemingly purposeless --log-fd=3 indirection.
this helps enormously on the first sync of a 100k message box with a
limit of 1k messages. it also happens to make the syncing idempotent.
in a few conditionals we now explicitly test for max_messages being
enabled, not smaxxuid != 0, as after the initial fetch with no important
messages smaxxuid is zero, but we still have to skip over 99k messages
in the above case.
the removed code would only ever trigger if a) we were after a journal
replay or b) something external expunged the expired messages - both are
corner cases not worth the extra code.
however, this means that the syncing code further down now needs to take
care of these zombies.
in the end, the normal cleanup will take care of all expired entries,
new and old.
the header is not space-critical, so use proper name-value pairs.
this has the additional advantage that subsequent format changes can be
done much easier.
this value is only ever used to find just pushed messages by TUID, so we
can simply use the UIDNEXT value from before we started pushing - and of
course, we need to record that in the journal. it makes no sense to log
the new value after completing a search, as there won't be a next search
before we push the next messages.
files may be renamed (due to new -> cur transition or flag changes),
which may lead to two effects if ignored:
- we see both the old and the new name, so we report a spurious
duplicate UID
- we see neither name, so we report a spurious deletion
as countermeasure, record and compare directory modification times. upon
mismatch, we just start over - as usual.
instead of SEARCHing every single message (which is slow and happens to
be unreliabe with M$ Exchange 2010), just FETCH the new messages from
the mailbox - the ones we just appended will be amongst them.
