Add checking for per-entry sizelimit (ITS#554)

[Kurt@OpenLDAP.org]

Though such a feature may be useful, your implementation is not
suitable for inclusion into OpenLDAP for the following reasons.

1) no dead lock prevention
2) assumes bind DN refers to an entry within same backend
   operation is being processed by
3) no access control applied

It is likely better to implement per-user (soft and hard?) limits
using variables associated with the session and populated at
bind time.  If you would like to work on such, please discuss and
coordinate on our developer list.

If you do not concur with this review, please post
a rebuttal to our developer list.

We do appreciate your efforts and hope you will see them
through.
	Kurt