support server side pagination

[graingert]

[fastrde]

I run into the same issue when i use ldaptor as a proxy. The problem is, that LDAPSearchRequest is handled by handleUnknown and then get executed via send_multiResponse and not send_multiResponse_ex. The controls with the pagination cookie didn't reach the proxied client.

I send you a pull request where i fixed that for my usecase. But i changed send_multiResponse to handle Responses with and without controls and removed send_multiResponse_ex, so it's most likely a breaking change.