back-sql enhancements

[Dmitry Kovalev <mitya@seismic.geol.msu.ru>]

Summary of recent updates to CVS version (hope they will get into 2.0.7)

- back-sql approved to work with unixODBC and EasySoft's OBDC-ODBC
bridge.  many thanks to Emile Heitor, isdnet.

   in summary, back-sql is reported by lots of people to work with:
        iODBC and unixODBC driver managers on Un*x, odbc32.dll on
Windows
        OpenLink's and EasySoft's access suites, and various standalone
drivers on Un*x and Windows
        Oracle 7/8, MS SQL Server 6.5/7, mySQL > 3.22.25, Teradata
RDBMSes
         (may be more - just mail ;)

- filter processing and translation to SQL fixed (no more crashes on
malformed filters - ITS #855, fixed case-insensitive matches on
case-sensitive RDBMSes like Oracle)
       thanks go to Mathieu Guillaume, Vox Mobili, for help in wiping
this out

- improvements in documentation, including some useful tricks suggested
by Robin Elfrink

- support for multiclassing (in addition to objectclass an entry maps to

SQL data, it can now have any number of "fake" objectclasses, and match
in queries for this objectclasses)

- support  for referrals, using multiclassing

- documentation and samples updated to these changes

todo:
  - password exop, for ldappasswd to work with back-sql, as requested by

Nick Bobuh
  - client IP and other useful parameters to be made available in SQL
queries, as requested by Robin Elfrink
  - entry caching to improve performance
  - alias support
  - further tests for memory leaks and other stability issues (can
anyone help with this?)

WBW, Dmitry