Bump junit from 4.7 to 4.13.1

Add support for turning on tcp keep alive.

SPY-195: Defer String Concat in handleEmptySelects()

SPY-194: Allow to optionally bound retry queue.

SPY-193: Allow to override wakeupDelay

SPY-192: Ensure connection key is valid before checking if writable.

SPY-191: Don't force reconnect on E2BIG with binary protocol.

SPY-190: Remove the no-operation isInterrupted() call. Document interruption policy.

SPY-187: Expose a few more attributes of MemcachedClient

Support Libmemcached ketama weighted

SPY-183: Allow touch operations to be cloned.

Fix spring unit tests.

SPY-181: GetAndLock needs to be cloneable like any other keyed op.

SPY-182: Avoid WARN logging when handling node not set.

Change MemcachedNodeROImpl and BaseGetOpImpl classes to public.