Fixup cb_cond_timedwait for pthread

Change-Id: I9428505bb44de5abd3df4e3947a0cd220b9d4f63
Reviewed-on: http://review.couchbase.org/30981
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>