bugfix: be more tolerant to malformed journal fields

This prevents a segfault when a malformed journal entry field doesn't
contain an equal sign. Should not ever happen but was actually
triggered by a real bug in systemd journal.
bugfix: prevent an endless loop in the ratelimiter

If messages are being dropped because of ratelimiting, an internal
message is generated to inform about this fact. This should happen
only uppon the firs occurance but the counter that tracks the number
of dropped messages was incremented only after sending the message. If
the message itself gets ratelimited, an endless loop spins out of
control. Thanks to Jerry James for notifying about this.
doc: add contributed patches to ChangeLog