CCBC-335: Provide lcb_config_refresh()

See the extensive header documentation as to why this is necessary.
Bundled with this change is the lcb_wait3() function which provides more
flexible modes for running the event loop.

Change-Id: I2947bdb822cda6282bf7c8dfa679d0f303e35796
Reviewed-on: http://review.couchbase.org/38300
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>