apr_dbd updates

[Nick Kew <ni...@webthing.com>]

I've made some more updates, mainly improvements to the API and
factoring out of differences between SQL syntaxes to improve
portability of applications (most importantly, my own:-)
I've also found and fixed the bug that was affecting the prepared
query test in the PostgreSQL driver.

I won't post all the code to the list again now, but anyone looking
at it, please let me know and I'll package an updated tarball.

-- 
Nick Kew