back overlay (ITS#2751)

[ando@sys-net.it]

Full_Name: Pierangelo Masarati
Version: HEAD
OS: Linux
URL: http://www.sys-net.it/~ando/Download/backover.c.ando-2003-10-05.patch
Submission from: (NULL) (81.72.89.40)
Submitted by: ando


This ITS is only to keep track of the changes I'm trying to set up before 
I commit anything.  While playing with overlays I noted that:

1) there is something I don't understand when dealing with "send entry"
   callbacks, which is fixed by the attached patch; or am I missing something?
2) the data this callback is seeing might be readonly, so we need a mechanism
   to prevent unwanted modifications and to allow needed modifications.
   I'm working at a DN rewrite/attribute map overlay that will allow to get
   rid of these specialized features in back-ldap/back-meta, while extending
   this capability to any backend.  I'll try to setup a mechanism to signal
   whether an entry can be modified or not, and, in case, to replace it with
   a copy.  After the entry is copied, the following overlays will be allowed
   to modify parts of it without the need to copy it again.  I won't set up
   any granular modificability indicator: as soon as part of an entry needs 
   be accessed, it gets entirely copied.

Ando.