Fixed the Rakefile's interaction with postgresql use PGPASSWORD and PGHOST in the environment to fix prompting for passwords when connecting to a remote db and local socket connections. Also added a '-x' flag to pg_dump which stops it dumping privileges #807 [rasputnik]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@931 5ecf4fe2-1ee6-0310-87b1-e25e094e27de