[development] update.php and postgres 7.4

[Brenda Wallace]

update.php from D5 to head doesn't work on pg7.4 - because you can't add
constraints or default in the same statement as column add.

Sure, it can be patched (and i've got one i'll submit) but how does the
project fee about dropping old 7.4 and requiring pg8.0? If not for D6
then at least D7. It's an easy upgrade path, and 8 is in most distros (i
dunno about redhat)