Note: this breaks LDAP_COMP_MATCH and SLAP_ZONE_MALLOC. But they
were probably broken already anyway.

since o_csn is always allocated on the thread's slab, and since CSNs always have the same length, reuse memory (part of o_csn memory handling cleanup)

remove syncrepl stuff from Operation struct

using the same op structure, such as in refint overlay, cause a memleak
otherwise.) Probably should be using tmpmem for this.

	- memory based session history to minimize sync traffic
	- when client is covered by a session history, then
      [add+delete] mode is used
	- when client cookie is not covered by the history because
      the cookie is too outdated and/or the history is truncated,
	  [add+present] mode is used
2. Sync cookie syntax : comma separated name=value pairs
	- csn=yyyymmddhh:mm:ssZ#0xSSSS#r#ssssr,sid=nnn