tiny patch to make vacuumdb -a's database order match pg_dumpall

Hiya,

I've been having trouble running vacuumdb -a and pg_dumpall
concurrently because they run through the databases in a different
order (so dumpall was getting stuck behind vacuum's lock, and my
firewall was rather unhelpfully closing the idle connection). I can't
see a good reason for them to be using a different order, and as it
will only affect those that have created new databases since restoring
from a dump, may not be instantly obvious. It appears slightly more
thought has gone into pg_dumpall's code (in that it actually includes
an ORDER BY), so I elected to fiddle with vacuumdb.

I hope this is in the correct format (this is the first patch I've
submitted for anything), please let me know if I've done something
daft.

Dan

237c237
<       result = executeQuery(conn, "SELECT datname FROM pg_database
WHERE datallowconn;", progname, echo);
---
>       result = executeQuery(conn, "SELECT datname FROM pg_database WHERE datallowconn ORDER BY 1;", progname, echo);