Postgres fix for drush sql dump

Okay, I'm embarrassed by this one. I fixed this bug previously, but somehow the fix was not in the patch I submitted; I just checked out drush HEAD and noticed that sql dump is broken for postgres. I'm not sure how I managed to submit the wrong thing.

The '-q' modification I put in for Postgres only applies to psql, not to pg_dump. If you run pg_dump with -q, you get an error and drush sql dump fails. This patch fixes the arguments for pg_dump so that -v is passed for verbose, and nothing is passed for normal operation.

Sorry about that,

- Greg