rabbitmq-server: new upstream release fixes serious bugs

Binary package hint: rabbitmq-server

There's a new release of RabbitMQ upstream, 1.5.4, and we'd like to try to get this into Jaunty if at all possible. I know it's rather late, however the release contains two fixes of serious bugs and all the changes are small, self-contained, have been tested thoroughly and are considered low-risk.

The serious bugs are:

- set the current working dir of the various scripts to /var/lib/rabbitmq
instead of /. The latter was preventing crash dumps from being written, which
made it very difficult to diagnose the root cause of any severe problems the
server may be encountering.

- starting a RabbitMQ instance that contains a large number (thousands) durable
exchanges, queues or bindings now takes just a few seconds instead of several
minutes. The latter was causing the startup scripts to erroneously report that
RabbitMQ failed to start, as well as causing operational problems due to
prolonged unavailability of the server on restart.

Both of these bugs have been reported by several users of the 1.5.3 release.

The release also contains two minor enhancements to the configurability of
RabbitMQ:

- make the default settings of the various env vars which can be set in
rabbitmq.conf visible to that script, thus permitting more advanced
manipulation of the settings than was previously possible.
- permit configuration of rabbitmqctl's Erlang start parameters by sourcing
rabbitmq.conf from the script and adding some env vars.

In combination these two enhancements resolve a long-standing user complaint:
that it wasn't possible to set the Erlang cookie to a fixed, common value
without editing the scripts. That is particularly problematic in a clustered
set up, where all machines need to have the same cookie in order for RabbitMQ's
clustering to work.