frontend stuff moved into a database structure, essentially to allow overlays to be processed before database selection; passes all tests (ITS#3080)

misc other cleanup

(slapi_x_XXX is still reserved for exported functions that are not part
of the SLAPI specification)

add to 'val[.<style>=<value>' ACLs special match styles for DN-valued attributes; add negated objectClass to attribute name lists for ACLs and partial replication

	- 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      the cookie is too outdated and/or the history is truncated,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

order to prevent the operation from being passed to the backend. It
need only return a non-zero error code.

replace calls to dnNormalize2 with calls to dnNormalize

dereference policy

Improved ch_malloc/sl_malloc compatibility.

breaks API compat

computed search rewriter plugins cannot use thread-local malloc

Needs work in normalizers, etc.