s4:samldb LDB module - simplify/unify the message handling on add and modify operations

s4:samldb LDB module - simplify/unify the message handling on add and modify operations

- Perform only shallow copies (should be enough)
- Perform only one copy per operation (also on modifications)
- Build a new request on modify operations if needed ("modified" flag) - this
  makes it look cleaner
- Fix an important bug: the "el" pointers could have changed after
  modifications. Therefore we have to refresh them on the FLAG_DELETE checks

Autobuild-User: Matthias Dieter Wallnöfer <mdw@samba.org>
Autobuild-Date: Tue Oct  5 09:24:57 UTC 2010 on sn-devel-104