PCBC-228: Preserve extra error information

Change-Id: Ib7964d6064dd7eaeeecd480610b26ca33327fcd4
Reviewed-on: http://review.couchbase.org/26224
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>