limit alpha->beta conversion through msg store credit flow
we also bump the IO_BATCH_SIZE; it's only used to limit beta->gamma
conversion, which is a fairly cheap operation (it only touches qi,
which has a very compact on-disk representation), and we want to make
sure that such conversion can keep up with the alpha->beta conversion.
merge in default
decouple syncing from paging
explain (reduced) impact of IO_BATCH_SIZE
propagate BQ API change
reduce_memory_use now only does one thing
increase IO_BATCH_SIZE
...so that beta->gamma conversion can keep up with alpha->beta
conversion.

Also correct comment - beta->gamma conversion can happen in a lot more
places than 'publish'
beta->delta conversion rate is naturally limited
which means we don't need an explicit upper bound, which in turn would
have required some interaction with q_process.
make tests work
- 'hole' generation is sensitive to IO_BATCH_SIZE
- need to handle credit bumps post publishing and prior to status
  checks
Get the leader to transition directly to winner or loser state if that's where it's going, or wait in a special lead_waiting status if neither, so that if we get any more autoheal requests we can ignore them.
Show the distribution port as a "protocol" in management.
Add listeners to rabbitmqctl status.
Slightly simpler, and more polite.
Improved diagnostics.
Try to be a bit less verbose.
Since we always show the raw error and the expanded error let's get format_inet_error to do that.
Various formatting tweaks.
Just in case the error is not an atom.
Set the distribution port range to the first of these that matches:

* Not at all if it's mentioned in the config file
* $DIST_PORT if that's mentioned in the env file
* $RABBITMQ_DIST_PORT if that is set
* $RABBITMQ_NODE_PORT + 20000 if that is set
* 25672 in all other cases
Don't suggest using the kernel params here.