Several updates to get server side sorting going:

Several updates to get server side sorting going:
- Added sort control to ads_do_paged_search.  It allows a char * to be passed
  as the sort key.  If NULL, no sort is done.
- fixed a bug in the processing of controls (loop wasn't incremented properly)
- Added ads_do_search_all2, which funs a function that is passed in against
  each entry.  No ldapmessage structures are returned.  Allows results to
  be processed as the come in on each page.

I'd like ads_do_search_all2 to replace ads_do_search_all, but there's some
work to be done in winbindd_ads.c first.

Also, perhaps now we can do async ldap searches?  Allow us to process a
page while the server retrieves the next one?