Update to 1.6.0.

And fix a test that depended on hash ordering.
Remove any JDBC drivers an app leaves registered on undeploy [IMMUTANT-417]

Leaving drivers registered can result in permgen leaks.
Test for the correct clojure version.
Must remove the cache in order to reconfigure it [IMMUTANT-423]
Don't attempt to show source links to protocol fns [IMMUTANT-420]

Protocol fn vars don't have line number meta, and they have no body,
so there's no point in linking to them. The protocol itself is still
linked.
Allow the same .ima to be mounted as multiple apps [IMMUTANT-412]
Added test for deploying the same .ima [IMMUTANT-412]
Force last value queues to not use paging [IMMUTANT-406]
Log message when unlistening [IMMUTANT-409]
Allow setting the thread count for the Quartz scheduler pool [IMMUTANT-415]
Note that :concurrency > 1 is a bad idea for topics [IMMUTANT-411]
Update api docs
Update the logic for initing a repl on deploy [IMMUTANT-416]

This change makes [:immutant :nrepl-port] override [:ring :nrepl]. The
init now works like this:

1) if no repl config is provided, a repl on port 0 will start in dev mode
2) if [:ring :nrepl] is provided, the repl will only start if [:ring :nrepl :start?]
3) if [:immutant :nrepl-port] is set, it overrides [:ring :nrepl]. If it is `nil`,
   no repl will be started, even in dev mode.
Doc ring nrepl options [IMMUTANT-402]
Remove unneeded at-exit references.
Remove unnecessary destination removal code.

Upon review, we determined this call would only ever get called when
two threads were competing for the lock around .destroyDestination,
and would have undefined behavior in that case. This section is likely
a holdover from before we required messaging/start to be called.
Don't register the same class at the same phase & priority as TorqueBox.

Doing so breaks overlay with our backports to AS7 to support running
on Java 8.
Leave things like you found them
Fixes IMMUTANT-324 regression from fix for IMMUTANT-423

No longer possible to get a stopped cache from lookup. It'll be started
if it's stopped.