repl: event ordering: delay 'close' until 'flushHistory'

Emitting 'close' before the history has flushed is somewhat incorrect
and rather confusing.

This also makes the 'close' event always asynchronous for consistency.

Refs: https://github.com/nodejs/node/pull/2356
PR-URL: https://github.com/nodejs/node/pull/3435


Reviewed By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>