Godeps/_workspace/src/gopkg.in/mgo.v2/session.go
func (s *Session) Clone() *Session {
	s.m.Lock()
	scopy := copySession(s, true)
	s.m.Unlock()
	return scopy
}
func (s *Session) Clone() *Session {
	s.m.Lock()
	scopy := copySession(s, true)
	s.m.Unlock()
	return scopy
}
// Clone works just like Copy, but also reuses the same socket as the original
// session, in case it had already reserved one due to its consistency
// guarantees.  This behavior ensures that writes performed in the old session
// are necessarily observed when using the new session, as long as it was a
// strong or monotonic session.  That said, it also means that long operations
// may cause other goroutines using the original session to wait.