Add include of stdio.h

Change-Id: I20efd3224b0d51ff7378b57f12a145dd04f5fbdd
Reviewed-on: http://review.couchbase.org/31572
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>