ITS#3707 filters

[hyc@symas.com]

I've had a patch for the Filter handling sitting here half-finished for 
quite a while. The intent is to preserve all of the original filter data 
so that it can be reused directly.

On a related note, RFC4511 changes the behavior of presence matching on 
unknown attributes to be Undefined now instead of FALSE. So presumably 
we should update our code accordingly.

-- 
   -- Howard Chu
   Chief Architect, Symas Corp.  http://www.symas.com
   Director, Highland Sun        http://highlandsun.com/hyc
   OpenLDAP Core Team            http://www.openldap.org/project/