Set a high priority on couch_server

In a VM with lots of processes couch_server can end up slowing down
purely to not being scheduled which in turn will cause its message queue
to backup. We've attempted this before but due to message passing have
never seen it have a significant effect. However, now that we're
actively avoiding synchronous message passing inside the man loop this
has a significant effect by being able to process messages as soon as it
has one in its mailbox.
3 files changed