DBI/SQL backend

[Phil Longstaff]

I think the DBI/SQL backend is ready to try.  It is in the gda-dev2
branch.  The GDA backend has been disabled and a DBI backend is enabled.
 It assumes that the include files are in /usr/include/dbi/dbi.h and the
driver files are in /usr/lib/dbd.  The only driver that the DBI backend
supports is sqlite3.  I am using libdbi-0.8.2.  I assume later versions
will work.  I don't know about earlier versions.  There is a compilation
check that the header file is present, but no version check.

No new URI types have been added.  If you try to open a file, it will
check if it is an sqlite3 file, and will load it with sqlite3.  If it
can't, it will revert to xml.  Save As will save a file as an sqlite3
file.  The "Connect to Database" menu entry is still enabled but will
(probably) fail.

I don't have a windows compilation environment, so I haven't tried it on
windows.

Please feel free to try it out and report any problems.  This is not yet
ready for your real data, though it would be a good test to load your
xml file and save-as an sqlite3 file.

Phil