LDAP paging support

[helix84]

Addresses issue #169.

The only drawback is that it hardcodes page size because I haven't figured out how to query the server for max. page size.

Compatibility: RFC 2696 (1999)

...
 An LDAP client application that needs to control the rate at which
   results are returned MAY specify on the searchRequest a
   pagedResultsControl
...
If the server does not support this control, the server
   MUST return an error of unsupportedCriticalExtension if the client
   requested it as critical, otherwise the server SHOULD ignore the
   control.
...

[helix84]

@rdunklau: Ping? Any chance of merging this? Thank you.